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47th Mersenne Prime Confirmed

kdawson posted more than 5 years ago | from the that's-odd dept.

Math 89

radiot88 writes to let us know that he heard a confirmation of the discovery of the 47th known Mersenne Prime on NPR's Science Friday (audio here). The new prime, 2^42,643,801 - 1, is actually smaller than the one discovered previously. It was "found by Odd Magnar Strindmo from Melhus, Norway. This prime is the second largest known prime number, a 'mere' 141,125 digits smaller than the Mersenne prime found last August. Odd is an IT professional whose computers have been working with GIMPS since 1996 testing over 1,400 candidates. This calculation took 29 days on a 3.0 GHz Intel Core2 processor. The prime was independently verified June 12th by Tony Reix of Bull SAS in Grenoble, France..."

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Cool processor (0)

Brian Gordon (987471) | more than 5 years ago | (#28323137)

They're crunching 13-million-digit numbers with a desktop processor? Do they realize that they can put eight quad-core xeons in a machine and finish the calculation in a single shift instead of waiting a month?

Re:Cool processor (5, Informative)

Jarlsberg (643324) | more than 5 years ago | (#28323151)

It was found through the GIMPS (The Great Internet Mersenne Prime Search). The site http://www.mersenne.org/prime.htm [mersenne.org] is currently down.

Re:Cool processor (5, Funny)

bergonom (1040428) | more than 5 years ago | (#28323319)

What are the odds this odd odd would be found by Odd?

Re:Cool processor (1, Insightful)

Anonymous Coward | more than 5 years ago | (#28323603)

*hands you the key to the city*

Re:Cool processor (1)

davidsyes (765062) | more than 5 years ago | (#28324679)

Quite oddly high, it seems... I guess it's not so odd anymore that he is an accomplished oddity...

Re:Cool processor (1)

Vintermann (400722) | more than 5 years ago | (#28327911)

They're about even [wikipedia.org] .

Why is this useful? (2, Insightful)

Abreu (173023) | more than 5 years ago | (#28323413)

The answer is not in the summary, nor in the first page of the FA...

Buried somewhere in the linked site is this FAQ:

http://primes.utm.edu/notes/faq/why.html [utm.edu]

However all the answers are a bit unsatisfactory, IMHO...

So, I ask the great Slashdot hive-mind... What are the practical applications of Mersenne Primes and why are people paying money to find them?

Re:Why is this useful? (1)

registrar (1220876) | more than 5 years ago | (#28323649)

They're not practical. They're fun. Lots of slashdotters probably cut their teeth trying to find odd Mersenne primes. That's good enough reason.

Re:Why is this useful? (0, Troll)

registrar (1220876) | more than 5 years ago | (#28323657)

Idiot. Not odd Mersenne primes. Odd perfect numbers which are interesting because they're not related to Mersenne primes.

Re:Why is this useful? (1, Funny)

Anonymous Coward | more than 5 years ago | (#28324629)

And nothing of value was found.

Re:Why is this useful? (3, Insightful)

Rockoon (1252108) | more than 5 years ago | (#28325729)

Well, for one thing if you need a prime divisor, 2^n-1 primes have some good properties...

Modulus or Division by such numbers can be accomplished with a few fast operations (bitwise Shift/And, a comparison, and maybe a subtraction) instead of a single very slow one (an actual division.)

Re:Why is this useful? (1)

skeeto (1138903) | more than 5 years ago | (#28368341)

What are the practical applications of Mersenne Primes and why are people paying money to find them?

Here's one: PRNGs [wikipedia.org] .

Re:Cool processor (1)

thebigbadme (194140) | more than 5 years ago | (#28328675)

crypto man, crypto.....

Re:Cool processor (4, Informative)

Kurusuki (1049294) | more than 5 years ago | (#28323161)

They're crunching 13-million-digit numbers with a desktop processor? Do they realize that they can put eight quad-core xeons in a machine and finish the calculation in a single shift instead of waiting a month?

I don't know about you, but the last 13 or so mersenne primes have been found using prime95 as a conduit for a mass distributed effort. I'm not sure where you live, but in most other places people can't just go out and put 8 quad-core xeons in a home machine.

Re:Cool processor (5, Funny)

Nutria (679911) | more than 5 years ago | (#28323245)

I'm not sure where you live

He lives at home with his parents (or maybe in a dormitory room) and doesn't have a clue as to what it actually costs to run a home.

Re:Cool processor (0)

Anonymous Coward | more than 5 years ago | (#28327683)

His income in 2007 was approx. 87k USD. I doubt he wants to live with his parents ;-)

http://www.skattelister.no/?do=more&k=1653&id=68efd64f02c00d7d8638a53bced8c66c&navn=odd [skattelister.no] magnar aasan strindmo

Re:Cool processor (1)

Nutria (679911) | more than 5 years ago | (#28330659)

I'm not referring to Odd Magnar Strindmo.

Re:Cool processor (3, Interesting)

Nutria (679911) | more than 5 years ago | (#28323229)

Do they realize that they can put eight quad-core xeons in a machine and finish the calculation in a single shift instead of waiting a month?

What makes you think they aren't?

And what makes you think this man would pony up the serious coin for such a beast just to find a prime number?

Re:Cool processor (1)

Nikker (749551) | more than 5 years ago | (#28324277)

You mean especially since the bounty for a prime [utm.edu] goes from $100K - $250K?

Re:Cool processor (2, Insightful)

ceoyoyo (59147) | more than 5 years ago | (#28324933)

You don't get the $100k by searching for one prime though. You've got to be the lucky one that does the month long calculation on the number that actually happens to be prime.

It's like the lottery. You can't make a profit at it unless you're lucky. Otherwise, some big company would come in, invest a few million in number crunching, and take home all the bounties.

Re:Cool processor (5, Informative)

JoshuaZ (1134087) | more than 5 years ago | (#28323231)

The system used for this is GIMPS, the Great Internet Mersenne Prime Search. The system uses a distributed computing system using unused computing power in personal computers to search for various candidate primes. Computers do one of two things: Either trying to factor candidate Mersenne numbers or running a Lucas-Lehmer test on candidates without any small prime factors (the Lucas-Lehmer test is a special primality test for Mersenne numbers that is very fast). They use modular arithmetic and a variant of the Fast Fourier Transform to handle the multiplications which might otherwise become too difficult. The procedure is naturally a problem that can be made into a parallel processing problem like this since there are so many different candidate numbers to look at.

The summary doesn't mention but it is worth noting that the Lucas-Lehmer test allows one to check the primality of Mersenne numbers (numbers of the form 2^p-1, p prime) much faster than you can test the primality of generic numbers (or almost any other specialized form). Thus, for most of the last hundred years the largest primes known have been Mersenne primes. Currently the largest known prime is a Mersenne prime and the next 4 largest are also Mersenne primes. The GIMPS website - http://mersenne.org/ [mersenne.org] has a lot more details of both the math and software and explains how you can join in to help the project.

BOINC (1)

Fissure_FS2 (220895) | more than 5 years ago | (#28327013)

It's disappointing that they're using a home-grown management software instead of BOINC [berkeley.edu] like many of the other distributed computing projects. I, for one, would be much more likely to add to the effort if I didn't have to worry about another piece of software and how it shared resources with the Einstein and Rosetta I'm already running.

Re:Cool processor (3, Insightful)

rbarreira (836272) | more than 5 years ago | (#28323453)

Do they realize that they can put eight quad-core xeons in a machine and finish the calculation in a single shift instead of waiting a month?

Do you realize that that's less efficient than using those 32 cores to calculate 32 independent numbers?

Re:Cool processor - No, they can't (3, Informative)

davmoo (63521) | more than 5 years ago | (#28323725)

Do they realize that they can put eight quad-core xeons in a machine and finish the calculation in a single shift instead of waiting a month?

No, they can't. Each iteration of the software requires the results of the previous iteration. It cannot easily be made to run like you want on multiple cores. The best they could do on the processor you describe is run 8 separate copies of the application, each taking one month to run...they could test 8 numbers at once, but they cannot test one number 8 times as fast.

Re:Cool processor - No, they can't (4, Informative)

rbarreira (836272) | more than 5 years ago | (#28323801)

Actually that's not exactly correct, each iteration is also parallelizable. Most of the work in an iteration is a FFT, which is parallelizable.

http://www.fftw.org/parallel/parallel-fftw.html [fftw.org]

It's less efficient to do this than using each core for one independent number, so it's only used if quick checking of a number is desired (for example, when double-checking a previously found prime number).

Re:Cool processor - No, they can't (1)

TapeCutter (624760) | more than 5 years ago | (#28325435)

"they could test 8 numbers at once, but they cannot test one number 8 times as fast."

Just because most searches use one number per core does not mean testing a single candidate can't be done very efficiently over multiple cores. You only have to think about the process for finding a prime, ie: testing factors, test if the candidate is it divisable by two, three, five, ect. The test for each factor is independent, so you COULD test 8 factors simultaneously, no?

The only communication between threads is a semaphore to say "stop, thread XYZ found an integer factor", if you want to be pedantic it's not 8X as fast but rather close to 8X as fast. I suggest the reason most implementations use one candidate per core is because most searches look at more than one candidate and the semaphore test makes the alternative implementation slightly less efficent.

Re:Cool processor - No, they can't (2, Informative)

smallfries (601545) | more than 5 years ago | (#28325649)

If you were going to test for primality by sieving then you could take a process that is millions of times slower than the primality test used, and speed it up by a factor of 8.

Instead the test being discussed performs a series of squares and modulo reductions. Each operand is dependent on the previous result - the entire computation is one long dependency chain and so cannot be split onto multiple cores in the way that you describe.

Although having said that, it all flips around again if you look inside the primitive operations that the primality tests uses. So they're using FFT based multiplication steps to do the squaring which obviously can be parallelised quite well..

Re:Cool processor - No, they can't (1)

TapeCutter (624760) | more than 5 years ago | (#28326003)

"Instead the test being discussed performs a series of squares and modulo reductions."

Thanks for showing an old dog a new trick. :)

Re:Cool processor - No, they can't (1)

rbarreira (836272) | more than 5 years ago | (#28326019)

The primality test for these Mersenne primes does not consist of sieving, that would be way too slow given the size of these numbers.

Instead, the Lucas-Lehmer test is used, a very simple iterative process which you can implement in a few lines of code in most programming languages. It's described here:

http://primes.utm.edu/mersenne/index.html#test [utm.edu]

Re:Cool processor - No, they can't - correction (1)

davmoo (63521) | more than 5 years ago | (#28323741)

My bad...I misread your processor description...I thought you said 8-core. My answer is still correct though, I just used the wrong number of copies. They can run one copy per core, and the copies cannot exchange information.

Re:Cool processor (3, Informative)

Daswolfen (1277224) | more than 5 years ago | (#28324461)

As one of the IT guys who maintain the lab that found the 43rd and 44th primes at University of Central Missouri (formerly CMSU), I can tell you its one number per core. Also, these are production machines in computer labs as well as classroom, faculty and staff systems that run the GIMPS software.

We are a public university, its not like we have extra $5k machines just sitting around crunching a number. BTW, the systems that found the 43rd and 44th prime numbers were base model Dell GX280s.

Re:Cool processor (1)

fuzzyfuzzyfungus (1223518) | more than 5 years ago | (#28336131)

I'm surprised that your 280s could take it. We have a load of those here and the PSUs are all starting to flake out. Even before that, the 280(desktop and SFF models anyway) is not what I'd call well ventilated.

Re:Cool processor (1)

Daswolfen (1277224) | more than 5 years ago | (#28342083)

These are all the tower models, which have better air flow. The problem is that systems of that era are subject to the burst capacitors (look for the ones with an X rather than a K or T) and we did have issues with that as well, but we preemptively replaced MBs and PSUs of the of the ones with failing capacitors before our warranty ran out.

As far as running the software, GIMPS is usually pretty good about sharing processor time, and some of the heavier use labs are scheduled to run 9pm-7am.

The nice part is we can crank out a lot of numbers when you have 500+ systems all running GIMPS in the background :)

Odd's prime (5, Funny)

fph il quozientatore (971015) | more than 5 years ago | (#28323155)

So, all primes greater than two are odd, but only one of them is Odd's!

Re:Odd's prime (1, Funny)

Snarf You (1285360) | more than 5 years ago | (#28323167)

I wonder what the odds were that he actually found it?

Re:Odd's prime (2, Funny)

Melkman (82959) | more than 5 years ago | (#28323257)

That's odd when you think about it.

Re:Odd's prime (5, Funny)

bcrowell (177657) | more than 5 years ago | (#28323575)

His brother, Even Magnar Strindmo, is also an IT professional. Even, like his brother Odd, has been testing candidates since 1996. The latest candidate in Even's search was 2^42,643,801-2, which was found to be composite. The very next number, 2^42,643,801-1, was the one his brother found to be prime. "Yeah, it kind of hurts to get so close and not be the one who got it," admits Even, "but I gave it my best game. We agreed back in '96 that we'd split up the work and go even-odd. I guess it was just a matter of luck that he got the first prime. I'm going to keep on trying, though. He's ahead now, 1-0, but if we keep going, I figure at some point I'll pull ahead."

Re:Odd's prime (1, Interesting)

Anonymous Coward | more than 5 years ago | (#28324139)

Hah, excellent. :)

(For the non-locals, Even is a perfectly common Norwegian name.)

Re:Odd's prime (0)

PyroMosh (287149) | more than 5 years ago | (#28325305)

I think you got the wrong joke.

Re:Odd's prime (1)

repvik (96666) | more than 5 years ago | (#28327645)

The fact that Odd and Even both are common norwegian names serves to make the joke a lot better (for us natives, that is).

Re:Odd's prime (1)

thebigbadme (194140) | more than 5 years ago | (#28329131)

I think he got the joke but decided to enrich people like me, who also got it, but didn't have as high an intrinsic response to the fact that an occurrence of having brothers named Even and Odd isn't out side every day possibility ... sort of like a British joke

Re:Odd's prime (1)

Man Eating Duck (534479) | more than 5 years ago | (#28333955)

A few people have both names as well; have a look at the Norwegian White Pages. [gulesider.no]
I can't help but think this is some kind of joke from the parents, most Norwegians are reasonably proficient in English.

pix plz (-1, Offtopic)

cupantae (1304123) | more than 5 years ago | (#28323181)

pix plz

The joys of untested code (5, Interesting)

tqft (619476) | more than 5 years ago | (#28323255)

The admins missed the prime for about a month
http://mersenneforum.org/showthread.php?t=11996 [mersenneforum.org]
Apparently the email that was supposed to be sent wasn't when the prime was reported

Re:The joys of untested code (1)

rbarreira (836272) | more than 5 years ago | (#28323567)

The code has been tested, as this is not the first prime numbers this project finds (far from it in fact).

Apparently it hasn't been tested enough though ;)

wikipedia article (-1, Redundant)

Anonymous Coward | more than 5 years ago | (#28323279)

The obligatory wikipedia entry on mersenne primes [wikipedia.org] . Come on, mods. Do your work properly.

"telescope" from Intel (2, Interesting)

moon3 (1530265) | more than 5 years ago | (#28323313)

Discovering a prime number that distant from the zero is like discovering a Pluto like planet in outer space. But instead of Hubble telescope you need a powerful mathematical one..

Buggers. (1)

2*2*3*75011 (900132) | more than 5 years ago | (#28323325)

My super-strong RSA encryption modulus was (2^43,112,609-1)*(2^42,643,801-1) and now it's broken. So much for 85,756,410-bit encryption.

Hmm (3, Informative)

Anenome (1250374) | more than 5 years ago | (#28323335)

I honestly forget why I'm supposed to care about Mersenne primes. Like, I read something about them awhile back, it was somewhat interesting... and then--yeah. So:

http://en.wikipedia.org/wiki/Mersenne_prime [wikipedia.org]
In mathematics, a Mersenne number is a positive integer that is one less than a power of two.

A Mersenne prime is a Mersenne number that is prime. As of June 2009[ref], only 47 Mersenne primes are known; the largest known prime number (243,112,609 1) is a Mersenne prime, and in modern times, the largest known prime has almost always been a Mersenne prime.[1] Like several previously-discovered Mersenne primes, it was discovered by a distributed computing project on the Internet, known as the Great Internet Mersenne Prime Search (GIMPS). It was the first known prime number with more than 10 million base-10 digits.

For those who can't even remember what a prime is, it's a number that can only be divided (evenly) by 1 and itself. Here's a list of the first primes: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97

The Mersenne primes are the largest known primes.

Prime numbers have applications in electronic security and encryption breaking. I'm not sure what other purpose there is to knowing them, other than knowing them. The Mersenne in particular seem to be merely mathematical curiosities right now.

I was much more excited by the discovery that the the Fibonnacci sequence is contained within the 1/89 calculation.
http://www.geom.uiuc.edu/~rminer/1over89/ [uiuc.edu]

Mersenne Primes correspond to Perfect Numbers (5, Informative)

JoshuaZ (1134087) | more than 5 years ago | (#28323485)

The historical reasons for caring about Mersenne Prime are twofold: First, Mersenne primes correspond to perfect numbers (numbers that are the sum of their positive less than the number. So for example, 6 has as proper divisors 1,2 and 3 and 1+2+3=6). The ancient Greeks were fascinated by perfect numbers but could not do much to understand them. Euclid showed that if one had a Mersenne prime one can construct an even perfect number. In particular, if 2^n-1 is prime then (2^n-1)*2^(n-1) is perfect. Almost 2000 years later, Euler showed that every even perfect number is of Euclid's form. Thus, investigating Mersenne primes tells us more about perfect numbers. The oldest unsolved problems in math are 1) are there any odd perfect numbers? and 2) are there infinitely many even perfect numbers? Thus, investigating Mersenne primes helps us get closer to solving one of the two oldest unsolved problems in mathematics.

Re:Mersenne Primes correspond to Perfect Numbers (0)

Anonymous Coward | more than 5 years ago | (#28323687)

I'm still lacking the point where I begin to care.

Re:Mersenne Primes correspond to Perfect Numbers (0)

Anonymous Coward | more than 5 years ago | (#28323865)

Then GTFO.

Re:Mersenne Primes correspond to Perfect Numbers (1)

Anonymous Coward | more than 5 years ago | (#28323759)

Well, I hate to break it to you, but you won't find any odd perfect numbers by finding Mersenne primes. (2^n-1)*2^(n-1) is going to be even for all n > 1.

Re:Mersenne Primes correspond to Perfect Numbers (1)

nacturation (646836) | more than 5 years ago | (#28325071)

Well, I hate to break it to you, but you won't find any odd perfect numbers by finding Mersenne primes. (2^n-1)*2^(n-1) is going to be even for all n > 1.

You missed that part where every even perfect number is of that form. It says nothing about what form odd perfect numbers take, if they exist at all.

Re:Mersenne Primes correspond to Perfect Numbers (2, Insightful)

Anenome (1250374) | more than 5 years ago | (#28323833)

Well, they may be unsolved problems, but again, they look like they have no relevance to anything, no application, other than being unanswered questions. But, like so many things, knowledge is valuable for its own sake, and who knows what revolution may result from what is now just a mathematical curiosity. Stealth-flight technology was originally harvested from a little known paper on radar written by an obscure Russian scientist. Kind of ironic that we were the ones to develop it. What you're really talking about is finding a proof for why there could or could not be any odd perfect numbers, and a proof for whether there are infinite perfect numbers or not. Typically, proofs like this that elude us lead into new forms, new paradigms of mathematics--which themselves result in great leaps forward in other areas once those proofs have been realized. That is certainly a story that has been repeated time and time again, most notably with calculus which is virtually the foundation of the modern world.

Even the concept of 'perfect numbers' is not familiar to me. Off to the Wiki!:

http://en.wikipedia.org/wiki/Perfect_number [wikipedia.org]
"In mathematics, a perfect number is defined as a positive integer which is the sum of its proper positive divisors, that is, the sum of the positive divisors excluding the number itself. Equivalently, a perfect number is a number that is half the sum of all of its positive divisors (including itself), or (n) = 2n.

The first perfect number is 6, because 1, 2, and 3 are its proper positive divisors, and 1 + 2 + 3 = 6. Equivalently, the number 6 is equal to half the sum of all its positive divisors: ( 1 + 2 + 3 + 6 ) / 2 = 6.

The next perfect number is 28 = 1 + 2 + 4 + 7 + 14. This is followed by the perfect numbers 496 and 8128 (sequence A000396 in OEIS).

These first four perfect numbers were the only ones known to early Greek mathematics."

Re:Mersenne Primes correspond to Perfect Numbers (0)

Anonymous Coward | more than 5 years ago | (#28324447)

Ok yeah, Mersenne primes relate to mathematically interesting topics. By why is it news every time someone discovers a new one? This contributes nothing (or very little) to the theory behind it all. Sure, eventually we may have enough for someone to see a new pattern in them or something. But one addition to the list doesn't help with that.

Re:Mersenne Primes correspond to Perfect Numbers (2, Insightful)

JoshuaZ (1134087) | more than 5 years ago | (#28324523)

Well, this does actually fit some of the patterns we are beginning to see. For example, there are reasons to expect that for most Mersenne primes 2^p-1 one will have p-1 having many small prime factors (this has to do with Fermat's Little Theorem). We in fact see that again in this case we see that since p-1 factors as 2^3 * 3^3 * 5^2 * 53 * 149. Also, the discoveries are are enough to be noteworthy in the same way that discovery of new elements is noteworthy. We likely won't find out much by itself from the discovery of element 117 when it occurs but it will be a big enough deal to get on Slashdot. Discoveries like these are sort of like summiting mountains. And for all we know, each one may be in fact be the last, since we can't prove there are infinitely many primes. Furthermore, primes in general are a fundamental building block of the integers. So finding very large ones is intrinsically cool.

Re:Mersenne Primes correspond to Perfect Numbers (1)

Anenome (1250374) | more than 5 years ago | (#28330629)

I would be rather surprised if there weren't an infinite number of primes, just based on the idea of what a prime is and how it's found. It's a sliver of a number, the falls between the divisable boundaries. And the larger the number get, it would seem, the more rare primes should become, this has certainly proven to be true. Hmm, that does seem to imply they would get more rare with time, since the more numbers you have as you increase the count, the more possible factors that exist. But still, that should only increase the period between existing prime.

Somewhere in there is a proof waiting to be discovered :P

Re:Mersenne Primes correspond to Perfect Numbers (1)

JoshuaZ (1134087) | more than 5 years ago | (#28330723)

We know there are infinitely many primes. This has been known since the ancient Greeks. Proving this is really easy: Assume there are only finitely many primes. Multiple them all together and add 1. This number is greater than 1 and not divisible by any prime number which is absurd. That's a contradiction so our original assumption is wrong and there are infinitely many primes.

What we can't show is that there are infinitely many Mersenne primes. A Mersenne prime is a prime that 1 less than a power of 2. Those are much harder to work with. We suspect that there are infinitely many. This is based on a rough probabilistic argument based on the Prime Number Theorem (a very deep result that gives good data about how many primes there are under a given real number x). But no one has any idea how to prove this.

Re:Mersenne Primes correspond to Perfect Numbers (1)

Hashi Lebwohl (997157) | more than 5 years ago | (#28330863)

Euclid proved it in approx 300BC
http://primes.utm.edu/notes/proofs/infinite/euclids.html

Re:Hmm (2, Interesting)

Bart Coppens (522625) | more than 5 years ago | (#28325795)

Actually, you can apparently use larger Mersenne Primes to improve results in totally different but very useful fields, like privacy-related schemes. For example, this paper http://eccc.hpi-web.de/eccc-reports/2006/TR06-127/index.html [hpi-web.de] uses large Mersenne primes to get interesting results on Locally Decodable Codes and Private Information Retrieval Schemes...

Can we have the value? (1)

selven (1556643) | more than 5 years ago | (#28323455)

My calculator doesn't show it, anyone have the value of the prime?

Re:Can we have the value? (3, Interesting)

spandex_panda (1168381) | more than 5 years ago | (#28323533)

This gives you the number [wolframalpha.com] , keep hitting 'More digits'. Unfortunately it gives it as an image so I can't copy paste here.

Re:Can we have the value? (1)

somersault (912633) | more than 5 years ago | (#28324399)

The image has an alt-text containing the same text as the image, so you can still copy and paste from the page source if you wish

Re:Can we have the value? (1)

vladsinger (1049918) | more than 5 years ago | (#28387913)

Or, amazingly enough, you could click on the image and use the handy little box that pops up with "copyable plaintext".

Re:Can we have the value? (1)

somersault (912633) | more than 5 years ago | (#28389105)

That would be too easy.

Re:Can we have the value? (3, Funny)

Eudial (590661) | more than 5 years ago | (#28323599)

In base 2, it's 1111[42,643,792 more 1:s]1111.
In base 16 it's 0xffff[2,665,229 more f:s]ffff.

Wolfram says so in 1 sec. (1)

spandex_panda (1168381) | more than 5 years ago | (#28323491)

Well I don't know why it took 29 days for the computer to tell him it was so, wolfram alpha told me it was prime in ~1 second. [wolframalpha.com]

On that note, I asked Wolfram the other day the tree in a forest thing and I finally have an answer! [wolframalpha.com]

Re:Wolfram says so in 1 sec. (0)

Anonymous Coward | more than 5 years ago | (#28323561)

Not so much for a bear's activity [wolframalpha.com] in the woods, however...

Re:Wolfram says so in 1 sec. (1)

ta bu shi da yu (687699) | more than 5 years ago | (#28326291)

At least it tries to given an answer on the swallow question [wolframalpha.com] .

Re:Wolfram says so in 1 sec. (1)

thebigbadme (194140) | more than 5 years ago | (#28329287)

I believe the question you should have asked goes something like this:

"If a bear takes a shit in the woods, does anyone care?"

At least that's how it was phrased where I grew up in Wisconsin.

Re:Wolfram says so in 1 sec. (1)

chill (34294) | more than 5 years ago | (#28323675)

Really? I don't see where it generates output.

Change the last digit of the power to a 0 and it quickly comes up with FALSE, but I never see a "TRUE" for the original question. Where is the answer?

Re:Wolfram says so in 1 sec. (1)

spandex_panda (1168381) | more than 5 years ago | (#28323695)

That funny E sign means 'element of a set' [techtarget.com] and the set is defined by that funny P sign, which means all primes. This means that Wolfram is saying that 2^42643792 -1 is a member of the set of prime numbers. See also how they know it is a prime. [wolfram.com]

Re:Wolfram says so in 1 sec. (1)

chill (34294) | more than 5 years ago | (#28323751)

Yes, I know that. :-)

What I'm saying is that is listed under "input". That indicates to me it was reformulating your English question into a proper mathematical statement. Nowhere do I see output.

Try it this way and you'll see what I'm looking for: http://www29.wolframalpha.com/input/?i=is+(2%5E42%2C643%2C800+-+1)+a+prime+number [wolframalpha.com]

The "input" statement is the same formulation, but there is now a "result" block which was missing from your query. That result states "False" as opposed to changing the element symbol to the not-an-element symbol (funny E with a line thru it, IIRC).

If you're right, and I'm wrong, then WA needs to fix their interface because it is unclear that it actually confirms your question or just gives up. I'd like to see a "Result" block that simply says "True", like it does with the false answer.

Re:Wolfram says so in 1 sec. (1)

rbarreira (836272) | more than 5 years ago | (#28323843)

Here is a result which says true:

http://www29.wolframalpha.com/input/?i=is+3+a+prime+number [wolframalpha.com]

I guess it knows (2^n-1) can only be a prime number if n is prime (that's a known theorem).

Re:Wolfram says so in 1 sec. (1)

chill (34294) | more than 5 years ago | (#28323875)

Thanks. That leads me to believe it didn't really do the original calculation, instead it just gave up quietly.

Of course, they could always "cheat". They could create a list of known Mersenne Primes and just check against that...

Re:Wolfram says so in 1 sec. (1)

rbarreira (836272) | more than 5 years ago | (#28323919)

It probably has a bunch of quick checks that can tell it "definitely not prime", "definitely prime" or just give up if none of the heuristics applies.

One of the checks they could add is the one you mentioned (a list of the known ones).

Re:Wolfram says so in 1 sec. (1)

spandex_panda (1168381) | more than 5 years ago | (#28324293)

Ah I see what you are saying now, and you are rbarreira is probably right, it has given up. I thought that the input region saying it was a member meant it was true... Oh well, I did think it was pretty impressive that it new so quick!

Re:Wolfram says so in 1 sec. (1)

spandex_panda (1168381) | more than 5 years ago | (#28324299)

Ah I see what you are saying now, and you are rbarreira is probably right, it has given up. I thought that the input region saying it was a member meant it was true... Oh well, I did think it was pretty impressive that it new so quick!

I meant "knew so quick".

Re:Wolfram says so in 1 sec. (1)

somersault (912633) | more than 5 years ago | (#28324477)

it has given up

Maybe if you gave it a month or two it would get back to you eventually ;)

Re:Wolfram says so in 1 sec. (1)

cocotoni (594328) | more than 5 years ago | (#28327647)

At this moment they still have not confirmed the 47th Mersenne prime in Alpha: 47th Mersenne prime [wolframalpha.com]

Further more, the 41st-46th primes are listed as conjectured.

If we consider the 40th Mersenne prime, 2^20996011-1 [wolframalpha.com] it gives the same result when checking its primeness (times out) [wolframalpha.com] .

Re:Wolfram says so in 1 sec. (0)

Anonymous Coward | more than 5 years ago | (#28323863)

It does *not* say so. It just reformats youir question mathematically. That's the INPUT you see. There is no output. Observe that if you type in another number (e.g. replace the -1 by 0 or by -3), then it will have an OUTPUT section as well.

Re:Wolfram says so in 1 sec. (0)

Anonymous Coward | more than 5 years ago | (#28327353)

Wolfram Alpha could not evaluate your question, so it only displays its interpretation of your input, which is the logical assertion that 2^blabla -1 is an element of the prime numbers. It does not evaluate this proposition to an output of TRUE or FALSE (although it can with several other changes, so I assume it has some quick algorithms to check with, but nothing processor intensive). For example, change the last two digits of the power to 71, and Wolfram|Alpha again cannot spit out TRUE or FALSE. I presume that I have not just discovered another Mersenne Prime so close to this new one.

And when they find the 50th... (1)

martas (1439879) | more than 5 years ago | (#28323909)

... the Great Old Ones will return, all life on earth will be destroyed.

Re:And when they find the 50th... (1, Funny)

Anonymous Coward | more than 5 years ago | (#28323985)

.. the Great Old Ones will return, all life on earth will be destroyed.

Oh, come on, Biden isn't that bad.

According to The Guide ... (1)

fahrbot-bot (874524) | more than 5 years ago | (#28325051)

According to the The Hitchhiker's Guide to the Galaxy, "Odd Magnar Strindmo" was a fourth generation accounting prefect on the third major planet of the second solar system in the first minor galactic cluster directly to the "left" of the vicinity of Betelgeuse - a star that has recently gone supernova. After achieving a modicum of fame for discovering the 47th known Mersenne Prime, during extended holiday on the, mostly harmless, planet named Earth, Mr Strindmo retired to a life of semi-luxury where he preferred to be called "Steve".

It was done with GIMPS (1)

selven (1556643) | more than 5 years ago | (#28326177)

I say the entire number was photoshopped.

English name, and other forms of the new Mersenne (1)

chongo (113839) | more than 5 years ago | (#28332499)

The link on the GIMPS home page [mersenne.org] points to where one may obtain the decimal digits of the new Mersenne Prime [isthe.com] . Other forms of this prime are available [isthe.com] :

The dashed form of the English name is available at assist those who might actually want to read all or part of the +324 Megabyte name. :-)

Obligatory Joke (0)

Anonymous Coward | more than 5 years ago | (#28340741)

So a couple decided to name their child "Odd". During his entire childhood, and sometimes during his adult life, Odd wad ostracized and bullied for his weird name.

Odd quickly grew to hate his name. When he wrote his will, he asked that nothing be written upon his tombstone, so that he would not, even in death, be remembered by that loathed name of "Odd".

Odd grew old and died. His children followed his wishes and placed a blank stone slab above his grave.

To this day, when people walked past his grave and its blank tombstone, they would remark, "Huh? That's odd."

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