The Largest Known Primes -- A Summary

  1. Introduction

An integer greater than one is called a prime number if its only positive divisors (factors) are one and itself.  For example, the prime divisors of 10 are 2 and 5; and the first six primes are 2, 3, 5, 7, 11 and 13.  (The first 10,000, and other lists are available).  The Fundamental Theorem of Arithmetic shows that the primes are the building blocks of the positive integers: every positive integer is a product of prime numbers in one and only one way, except for the order of the factors. (This is the key to their importance: the prime factors of an integer determines its properties.)

The ancient Greeks proved (ca 300 BC) that there were infinitely many primes and that they were irregularly spaced (there can be arbitrarily large gaps between successive primes).  On the other hand, in the nineteenth century it was shown that the number of primes less than or equal to n approaches n/(ln n) (as n gets very large); so a rough estimate for the nth prime is n ln n (see the document "How many primes are there?")

The Sieve of Eratosthenes is still the most efficient way of finding all very small primes (e.g., those less than 1,000,000).  However, most of the largest primes are found using special cases of Lagrange's Theorem from group theory.  See the separate documents on proving primality for more information.

In 1984 Samuel Yates defined a titanic prime to be any prime with at least 1,000 digits [Yates84, Yates85].  When he introduced this term there were only 110 such primes known; now there are over 1000 times that many!  And as computers and cryptology continually give new emphasis to search for ever larger primes, this number will continue to grow.

If you want to understand a building, how it will react to weather or fire, you first need to know what it is made of. The same is true for the integers--most of their properties can be traced back to what they are made of: their prime factors. For example, in Euclid's Geometry (over 2,000 years ago), Euclid studied even perfect numbers and traced them back to what we now call Mersenne primes.

"The problem of distinguishing prime numbers from composite numbers and of resolving the latter into their prime factors is known to be one of the most important and useful in arithmetic.  It has engaged the industry and wisdom of ancient and modern geometers to such an extent that it would be superfluous to discuss the problem at length...  Further, the dignity of the science itself seems to require that every possible means be explored for the solution of a problem so elegant and so celebrated." (Carl Friedrich Gauss, Disquisitiones Arithmeticae, 1801)

See the FAQ for more information on why we collect these large primes!

  2. The "Top Ten" Record Primes

The largest known prime has almost always been a Mersenne prime.  Why Mersennes?  Because the way the largest numbers N are proven prime is based on the factorizations of either N+1 or N-1. For Mersennes the factorization of N+1 is as trivial as possible--a power of two!

The Great Internet Mersenne Prime Search (GIMPS) was launched by George Woltman in early 1996, and has had a virtual lock on the largest known prime since then.  This is because its excellent free software is easy to install and maintain, requiring little of the user other than watch and see if they find the next big one and maybe win some EFF prize money!

Any record in this list of the top ten is a testament to the incredible amount of work put in by the programmers, project directors (GIMPS, Seventeen or Bust, Generalized Fermat Search...), and the tens of thousands of enthusiasts!

rank	prime	digits	who	when	comment
1	2136279841-1	41024320	MP1	2024	Mersenne 52??
2	282589933-1	24862048	G16	2018	Mersenne 51??
3	277232917-1	23249425	G15	2018	Mersenne 50??
4	274207281-1	22338618	G14	2016	Mersenne 49??
5	257885161-1	17425170	G13	2013	Mersenne 48
6	243112609-1	12978189	G10	2008	Mersenne 47
7	242643801-1	12837064	G12	2009	Mersenne 46
8	5166932097152-5166931048576+1	11981518	L4561	2023	Generalized unique
9	4658592097152-4658591048576+1	11887192	L4561	2023	Generalized unique
10	237156667-1	11185272	G11	2008	Mersenne 45

Click here to see the one hundred largest known primes. You might also be interested in seeing the graph of the size of record primes by year: throughout history or just in the last decade.

Twin primes are primes of the form p and p+2, i.e., they differ by two.  It is conjectured, but not yet proven, that there are infinitely many twin primes (the same is true for all of the following forms of primes).  Because discovering a twin prime actually involves finding two primes, the largest known twin primes are substantially smaller than the largest known primes of most other forms.

rank	prime	digits	who	when	comment
1	2996863034895·21290000-1	388342	L2035	2016	Twin (p)
2	3756801695685·2666669-1	200700	L1921	2011	Twin (p)
3	66982155216384-6698215528192-1	144605	A18	2024	Twin (p)
4	22271030616384-2227103068192-1	136770	A13	2024	Twin (p)
5	65516468355·2333333-1	100355	L923	2009	Twin (p)
6	201926367·2266668-1	80284	A25	2024	Twin (p)
7	160204065·2262148-1	78923	L5115	2021	Twin (p)
8	18936119858192-18936119854096-1	76000	A13	2024	Twin (p)
9	15891732708192-15891732704096-1	75376	A22	2024	Twin (p)
10	9960942348192-9960942344096-1	73715	A18	2024	Twin (p)

Click here to see all of the twin primes on the list of the Largest Known Primes.

Note: The idea of prime twins can be generalized to prime triplets, quadruplets; and more generally, prime k-tuplets.  Tony Forbes keeps a page listing these records.

Mersenne primes are primes of the form 2^p-1.  These are the easiest type of number to check for primality on a binary computer so they usually are also the largest primes known.  GIMPS is steadily finding these behemoths!

rank	prime	digits	who	when	comment
1	2136279841-1	41024320	MP1	2024	Mersenne 52??
2	282589933-1	24862048	G16	2018	Mersenne 51??
3	277232917-1	23249425	G15	2018	Mersenne 50??
4	274207281-1	22338618	G14	2016	Mersenne 49??
5	257885161-1	17425170	G13	2013	Mersenne 48
6	243112609-1	12978189	G10	2008	Mersenne 47
7	242643801-1	12837064	G12	2009	Mersenne 46
8	237156667-1	11185272	G11	2008	Mersenne 45
9	232582657-1	9808358	G9	2006	Mersenne 44
10	230402457-1	9152052	G9	2005	Mersenne 43

See our page on Mersenne numbers for more information including a complete table of the known Mersennes.  You can also help fill in the gap by joining the Great Internet Mersenne Prime Search.

Euclid's proof that there are infinitely many primes uses numbers of the form n#+1.   Kummer's proof uses those of the form n#-1.  Sometimes students look at these proofs and assume the numbers n#+/-1 are always prime, but that is not so.  When numbers of the form n#+/-1 are prime they are called primorial primes.  Similarly numbers of the form n!+/-1 are called factorial primes.  The current record holders and their discoverers are:

Click here to see all of the known primorial, factorial and multifactorial primes on the list of the largest known primes.

A Sophie Germain prime is an odd prime p for which 2p+1 is also prime.  These were named after Sophie Germain when she proved that the first case of Fermat's Last Theorem (xⁿ+yⁿ=zⁿ has no solutions in non-zero integers for n>2) for exponents divisible by such primes.  Fermat's Last theorem has now been proved completely by Andrew Wiles.

Click here to see all of the Sophie Germain primes on the list of Largest Known Primes.

  3. Other Sources of Large Primes

Because of the lag time between writing and printing, books can never keep up with the current prime records (that is why this page exists!)  However books can provide the mathematical theory behind these records much better than a limited series of web pages can.  Recently there have been quite a number of excellent books published on primes and primality proving.  Here are some of my favorite:

• P. Ribenboim, The new book of prime number records, 3rd edition, Springer-Verlag, New York, 1995. (QA246 .R472).
• P. Ribenboim, The little book of bigger primes, Springer-Verlag, New York, 2004.  (A less mathematical version of the above text.)
• H. Riesel, Prime numbers and computer methods for factorization, Progress in Mathematics volume 126, Birkäuser Boston, 1994.
• R. Crandall and C. Pomerance, Prime numbers: a computational perspective, Springer-Verlag, New York, 2001.  ISBN 0-387-94777-9.

See also [Bressoud89] and [Cohen93] on the page of partially annotated prime references.  Also of interest is the Cunningham Project, an effort to factor the numbers in the title of the following book.

• J. Brillhart, et al., Factorizations of bⁿ±1 b = 2,3,5,6,7,10,11,12 up to high powers , American Mathematical Society, 1988 [BLSTW88].