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The Great Internet Mersenne Prime Search (GIMPS) is a collaborative project of volunteers who use freely available software to search for Mersenne prime numbers.
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The GIMPS project was founded by George Woltman, who also wrote the software Prime95 and MPrime for the project. Scott Kurowski wrote the PrimeNet Internet server that supports the research to demonstrate Entropia-distributed computing software, a company he founded in 1997. GIMPS is registered as Mersenne Research, Inc. Kurowski is Executive Vice President and board director of Mersenne Research Inc. GIMPS is said to be one of the first large scale distributed computing projects over the Internet for research purposes.
The project has found a total of fifteen Mersenne primes as of January 2016, thirteen of which were the largest known prime number at their respective times of discovery. The largest known prime as of January 2016 is 274,207,281 − 1 (or M74,207,281 in short). This prime was discovered on September 17, 2015 by Curtis Cooper at the University of Central Missouri.
To perform its testing, the project relies primarily on Lucas–Lehmer primality test, an algorithm that is both specialized to testing Mersenne primes and particularly efficient on binary computer architectures. They also have a trial division phase, used to rapidly eliminate Mersenne numbers with small factors which make up a large proportion of candidates. Pollard's p - 1 algorithm is also used to search for larger factors.
History
The project began in early January 1996, with a program that ran on i386 computers. The name for the project was coined by Luther Welsh, one of its earlier searchers and the discoverer of the 29th Mersenne prime. Within a few months, several dozen people had joined, and over a thousand by the end of the first year. Joel Armengaud, a participant, discovered the primality of M1,398,269 on November 13, 1996.
Status
As of March 2013, GIMPS has a sustained aggregate throughput of approximately 137.023 TFLOP/s. In November 2012, GIMPS maintained 95 TFLOP/s, theoretically earning the GIMPS virtual computer a place among the TOP500 most powerful known computer systems in the world. Also theoretically, in November 2012, the GIMPS held a rank of 330 in the TOP500. The preceding place was then held by an 'HP Cluster Platform 3000 BL460c G7' of Hewlett-Packard. As of November 2014 TOP500 results, these old GIMPS numbers would no longer make the list.
Previously, this was approximately 50 TFLOP/s in early 2010, 30 TFLOP/s in mid-2008, 20 TFLOP/s in mid-2006, and 14 TFLOP/s in early 2004.
Software license
Although the GIMPS software's source code is publicly available, technically it is not free software, since it has a restriction that users must abide by the project's distribution terms if the software is used to discover a prime number with at least 100 million decimal digits and wins the $150,000 USD bounty offered by the Electronic Frontier Foundation, and a bounty of $250,000 USD for a prime number with at least 1 billion decimal digits.
Third-party programs for testing Mersenne numbers, such as Mlucas and Glucas (for non-x86 systems), do not have this restriction.
Also, GIMPS "reserves the right to change this EULA without notice and with reasonable retroactive effect."
Primes found
All Mersenne primes are in the form Mq, where q is the (prime) exponent. The prime number itself is 2q − 1, so the smallest prime number in this table is 21398269 − 1.
Mn is the rank of the Mersenne prime based on its exponent.
^ † As of March 7, 2017, 39,213,959 is the largest exponent below which all other exponents have been checked twice, so it is not verified whether any undiscovered Mersenne primes exist between the 45th (M37156667) and the 49th (M74207281) on this chart; the ranking is therefore provisional. Furthermore, 70,679,269 is the largest exponent below which all other exponents have been tested at least once, so some Mersenne numbers between the 48th (M57885161) and the 49th (M74207281) have yet to be tested.
^ ‡ The number M74207281 has 22,338,618 decimal digits. To help visualize the size of this number, a standard word processor layout (50 lines per page, 75 digits per line) would require 5,957 pages to display it. If one were to print it out using standard printer paper, single-sided, it would require approximately 12 reams of paper.
Whenever a possible prime is reported to the server, it is verified first before it is announced. The importance of this was illustrated in 2003, when a false positive was reported to possibly be the 40th Mersenne prime but verification failed.