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Great Internet Mersenne Prime Search
Finding World Record Primes Since 1996
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Welcome to GIMPS, the Great Internet Mersenne Prime Search

To join GIMPS,

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Previous Day Stats
First Prime Tests642
Verified Prime Tests288
Newly Factored283

All exponents below 48 210 427 have been tested and verified.
All exponents below 85 526 383 have been tested at least once.

GIMPS 2019 fundraiser

GIMPS is a victim of its own success! In 2008, after claiming the EFF award for discovery of the first 10 million digit prime, GIMPS had about $25,000 cash on hand to fund the server hardware, ISP fees, and $3000 awards for discovery of new Mersenne primes. Due to the unexpected, but welcome, discovery of 6 new Mersenne primes since 2008, GIMPS now has enough cash to fund just two years of ISP fees (much less if a new Mersenne prime is discovered).

GIMPS needs your help! For the first time in our 23 year history we are conducting a fundraiser. Our goal is to raise $5000 or more in 2019 to build a better cushion for upcoming ISP expenses and cover the next prime discovery award. Please consider making a donation so GIMPS can continue its quest to discover ever larger Mersenne primes for years to come.

GIMPS has set up a new subforum where the board of directors will keep our users well informed of its decisions, past and present finances, and fundraising progress.

Prime95 version 29.8 - Recommended update

Version 29.8 (build 6) is the latest version available for download.

Highlights of version 29.8 include

You can view the full list of changes in the version history file here.

51st Known Mersenne Prime Found!

December 21, 2018 — The Great Internet Mersenne Prime Search (GIMPS) has discovered the largest known prime number, 282,589,933-1, having 24,862,048 digits. A computer volunteered by Patrick Laroche from Ocala, Florida made the find on December 7, 2018. The new prime number, also known as M82589933, is calculated by multiplying together 82,589,933 twos and then subtracting one. It is more than one and a half million digits larger than the previous record prime number.

GIMPS has been on amazing lucky streak finding triple the expected number of new Mersenne primes -- a dozen in the last fifteen years. This prime was even luckier for Patrick Laroche, striking pay dirt on just his fourth try. For years, Patrick had used GIMPS software as a free "stress test" for his computer builds. Less than four months ago he started prime hunting on his media server to give back to the project. By way of comparison, some GIMPS participants have searched for more than 20 years with tens of thousands of attempts but no success. This proves that, with luck, anyone can find the next new Mersenne prime.

The new prime is only the 51st known Mersenne prime ever discovered. Mersenne primes were named for the French monk Marin Mersenne, who studied these numbers more than 350 years ago. GIMPS, founded in 1996, has discovered the last 17 Mersenne primes. Volunteers download a free program to search for these primes, with a cash award offered to anyone lucky enough to find a new prime. Prof. Chris Caldwell maintains an authoritative web site on the largest known primes, and has an excellent history of Mersenne primes.

Patrick is one of thousands of volunteers using free GIMPS software available at Credit for this prime goes not only to Patrick Laroche for running the Prime95 software, Woltman for writing the software, Blosser for keeping the Primenet server running smoothly, and the thousands of GIMPS volunteers that sifted through millions of non-prime candidates.  In recognition of all the above people, official credit for this discovery goes to "P. Laroche, G. Woltman, A. Blosser, et al."

You can read a little more in the press release.

All tests smaller than M(43112609) have been verified, officially making it the 47th Mersenne Prime

April 8, 2018 — Nearly 9 years ago in August 2008, M(43112609) was discovered, and now GIMPS has finished verification testing on every smaller Mersenne number. With no smaller primes found, M(43112609) is officially the 47th Mersenne prime.

At the time of the discovery, M(43112609) was actually the 45th known Mersenne prime because M(37156667) wasn't discovered until 2 weeks later, and M(42643801) was found nearly a year later in June of 2009! The last time a Mersenne prime was discovered out of order was in 1988 when M(110503) was found over 4 years after M(132049), and in 1961 M(4423) was discovered mere seconds before M(4253) because of the order in which the printout was read.

This highlights the importance of waiting until all smaller exponents have been tested and verified before we can say definitively where any Mersenne prime is ranked. Due to the distributed nature of the project as a whole, numbers are not always tested in order and a smaller Mersenne prime may yet be found. For that reason, thanks to all the GIMPS members that contributed their resources towards achieving this milestone. Join now to help GIMPS press onward with verification tests to prove M(57885161) is the 48th Mersenne prime!

All tests smaller than M(42643801) have been verified, officially making it the 46th Mersenne Prime

February 22, 2018 — Nearly 9 years ago in June 2009, M(42643801) was discovered, and now GIMPS has finished verification testing on every smaller Mersenne number. With no smaller primes found, M(42643801) is officially the 46th Mersenne prime. Thanks to all the GIMPS members that contributed their resources towards achieving this milestone. Join now to help GIMPS press onward with verification tests to prove M(43112609) is the 47th Mersenne prime.

Verification tests are an important part of the GIMPS project. Errors can occur during a test of smaller numbers, invalidating the end result. Only by doing a double-check with matching results are we able to say for sure that a Mersenne number is composite. Until all numbers below a Mersenne prime have been verified, we don't know for sure if it's the 46th known Mersenne prime or if there might be a smaller one that we missed due to a machine error, so we at GIMPS celebrate these important verification milestones.

50th Known Mersenne Prime Found!

January 3, 2018 — Persistence pays off. Jonathan Pace, a GIMPS volunteer for over 14 years, discovered the 50th known Mersenne prime, 277,232,917-1 on December 26, 2017. The prime number is calculated by multiplying together 77,232,917 twos, and then subtracting one. It weighs in at 23,249,425 digits, becoming the largest prime number known to mankind. It bests the previous record prime, also discovered by GIMPS, by 910,807 digits.

Just how big is a 23,249,425 digit number? It's huge!! Big enough to fill an entire shelf of books totalling 9,000 pages! If every second you were to write five digits to an inch then 54 days later you'd have a number stretching over 73 miles (118 km) -- almost 3 miles (5 km) longer than the previous record prime.

Jonathan Pace is a 51 year old Electrical Engineer living in Germantown Tennessee. He is a long-time math enthusiast now working at FedEx and active in community charities. As SysAdmin for his charities, he runs Prime95 on all PCs and servers because GIMPS emails him if one doesn't check in, which is helpful for monitoring these remote computers from home or work. The PC that found the new prime took six days of intense computation on a quad-core Intel i5-6600 CPU to prove the number prime.

To be thorough, the prime number was independently verified with four different programs running on various hardware configurations.

In recognition of the individual discoverer, the software authors, the GIMPS project leaders, and every GIMPS participant's contribution, credit for the new prime goes to "Jonathan Pace, George Woltman, Scott Kurowski, Aaron Blosser, et al.".

Could you be the next lucky volunteer to discover a brand new Mersenne Prime? You'll need a reasonably modern PC and the free software on the download page.

You can read a little more in the press release.

49th Known Mersenne Prime Found!

January 7, 2016 — GIMPS celebrated its 20th anniversary with the discovery of the largest known prime number, 274,207,281-1. Curtis Cooper, one of many thousands of GIMPS volunteers, used one of his university's computers to make the find. The prime number, also known as M74207281, is calculated by multiplying together 74,207,281 twos then subtracting one. It has 22,338,618 digits -- almost 5 million digits longer than the previous record prime number

Dr. Cooper is a professor at the University of Central Missouri. This is the fourth record prime for Dr. Cooper and his university. The primality proof took a month of computing on a PC with an Intel I7-4790 CPU.  Dr. Cooper and the University of Central Missouri is the largest contributor of CPU time to the GIMPS project. The discovery is eligible for a $3,000 GIMPS research discovery award.

You can learn more in the press release or watch the standupmaths interview with Curtis Cooper regarding his discovery:

New Assignment and Recycling Rules

February 2014 — Since 2008, GIMPS has given users one year to complete assignments. This rule has not been enforced. This has held up completing milestones as some assignments did not complete even after several years.

During February 2014, new assignment and recycling policies were put in place to help GIMPS make steady progress on milestones by detecting assignments that are proceeding extremely slowly or not at all.

This affects users in two ways:

Users testing 100 million digit numbers are not affected by these new rules. Assignments made prior to March 1, 2014 will be given a year, as promised, to complete (plus a grace period if the assignment is close to complete).

More News and Discussions

GIMPS forumsHere you can chat with fellow GIMPS members, get help with installation questions, learn more about how GIMPS works, etc.

Make Math History!!

You could discover one of the most coveted finds in all of Mathematics - a new Mersenne prime number. We've found fifteen already. Join in on this fun, yet serious research project. All you need is a personal computer, patience, and a lot of luck.

In addition to the joy of making a mathematical discovery, you could win a (USD) $3,000 cash GIMPS Research Discovery Award for each Mersenne prime discovered, and the Electronic Frontier Foundation is offering a $150,000 award to the first person or group to discover a 100 million digit prime number! See how GIMPS will distribute this award if we are lucky enough to find the winning 100 million digit prime.

What are Mersenne primes and why do we search for them?

Prime numbers have long fascinated amateur and professional mathematicians. An integer greater than one is called a prime number if its only divisors are one and itself. The first prime numbers are 2, 3, 5, 7, 11, etc. For example, the number 10 is not prime because it is divisible by 2 and 5. A Mersenne prime is a prime of the form 2P-1. The first Mersenne primes are 3, 7, 31, 127 (corresponding to P = 2, 3, 5, 7). There are only 49 known Mersenne primes.

GIMPS, the Great Internet Mersenne Prime Search, was formed in January 1996 to discover new world-record-size Mersenne primes. GIMPS harnesses the power of thousands of small computers like yours to search for these "needles in a haystack".

Most GIMPS members join the search for the thrill of possibly discovering a record-setting, rare, and historic new Mersenne prime. Of course, there are many other reasons.

Last Updated April, 2019