A big 2 is a big prime!

The Largest Known Primes--A Summary

(A historic Prime Page resource since 1994!)
Last modified: 04:50:21 AM Monday November 18 2019 UTC

New record prime (GIMPS): 282,589,933-1 with 24,862,048 digits by P. Laroche, G. Woltman, A. Blosser, et al. (7 Dec 2018).


  1. Introduction (What are primes? Who cares?)
  2. The Top Ten Record Primes:
        largest, twin, Mersenne, primorial & factorial, and Sophie Germain
  3. The Complete List of the Largest Known Primes
  4. Other Sources of Prime Information
  5. Euclid's Proof of the Infinitude of Primes

Primes: [ Home || Largest | Proving | How Many? | Mersenne | Glossary | Mailing List ]

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Note: The correct URL for this page is http://primes.utm.edu/largest.html. The site The Top Twenty is a greatly expanded version of this information. This page summarizes the information on the list of 5000 Largest Known Primes (updated hourly).  The complete list of is available in several forms.

[up]   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/(log n) (as n gets very large); so a rough estimate for the nth prime is n log 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.   Before long we expect to see the first twenty-five million digit prime.

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 infrmation on why we collect these large primes!

[up]   2. The "Top Ten" Record Primes

The Ten Largest Known Primes See also the page: The top 20: largest known 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, and 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!

rankprime digitswhowhenreference
1282589933-1 24862048 G162018 Mersenne 51??
2277232917-1 23249425 G152018 Mersenne 50??
3274207281-1 22338618 G142016 Mersenne 49??
4257885161-1 17425170 G132013 Mersenne 48?
5243112609-1 12978189 G102008 Mersenne 47
6242643801-1 12837064 G122009 Mersenne 46
7237156667-1 11185272 G112008 Mersenne 45
8232582657-1 9808358 G92006 Mersenne 44
910223·231172165+1 9383761 SB122016
10230402457-1 9152052 G92005 Mersenne 43

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.

The Ten Largest Known Twin Primes See also the page: The top 20: twin primes,
and the glossary entry: twin primes.
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.

rankprime digitswhowhenreference
12996863034895·21290000+1 388342 L20352016 Twin (p+2)
22996863034895·21290000-1 388342 L20352016 Twin (p)
33756801695685·2666669+1 200700 L19212011 Twin (p+2)
43756801695685·2666669-1 200700 L19212011 Twin (p)
565516468355·2333333+1 100355 L9232009 Twin (p+2)
665516468355·2333333-1 100355 L9232009 Twin (p)
712770275971·2222225+1 66907 L5272017 Twin (p+2)
812770275971·2222225-1 66907 L5272017 Twin (p)
970965694293·2200006+1 60219 L952016 Twin (p+2)
1070965694293·2200006-1 60219 L952016 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.

The Ten Largest Known Mersenne Primes See also the pages: The top 20: Mersenne primes,
and Mersenne primes (history, theorems and lists).
Mersenne primes are primes of the form 2p-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!

rankprime digitswhowhenreference
1282589933-1 24862048 G162018 Mersenne 51??
2277232917-1 23249425 G152018 Mersenne 50??
3274207281-1 22338618 G142016 Mersenne 49??
4257885161-1 17425170 G132013 Mersenne 48?
5243112609-1 12978189 G102008 Mersenne 47
6242643801-1 12837064 G122009 Mersenne 46
7237156667-1 11185272 G112008 Mersenne 45
8232582657-1 9808358 G92006 Mersenne 44
9230402457-1 9152052 G92005 Mersenne 43
10225964951-1 7816230 G82005 Mersenne 42

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.

The Ten Largest Known Factorial/Primorial Primes See also: The top 20: primorial and factorial primes,
and the glossary entries: primorial, factorial.
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:

rankprime digitswhowhenreference
11098133#-1 476311 p3462012 Primorial
2843301#-1 365851 p3022010 Primorial
3392113#+1 169966 p162001 Primorial
4366439#+1 158936 p162001 Primorial
5145823#+1 63142 p212000 Primorial
642209#+1 18241 p81999 Primorial
724029#+1 10387 C1993 Primorial
823801#+1 10273 C1993 Primorial
918523#+1 8002 D1989 Primorial
1015877#-1 6845 CD1992 Primorial

rankprime digitswhowhenreference
1208003!-1 1015843 p3942016 Factorial
2150209!+1 712355 p32011 Factorial
3147855!-1 700177 p3622013 Factorial
4110059!+1 507082 p3122011 Factorial
5103040!-1 471794 p3012010 Factorial
694550!-1 429390 p2902010 Factorial
734790!-1 142891 p852002 Factorial
826951!+1 107707 p652002 Factorial
921480!-1 83727 p652001 Factorial
106917!-1 23560 g11998 Factorial

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

The Ten Largest Known Sophie Germain Primes See also the page: The top 20: Sophie Germain,
and the glossary entry: Sophie Germain Prime.
A Sophie Germain prime is an odd prime p for which 2p+1 is also a 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.

rankprime digitswhowhenreference
12618163402417·21290000-1 388342 L9272016 Sophie Germain (p)
218543637900515·2666667-1 200701 L24292012 Sophie Germain (p)
3183027·2265440-1 79911 L9832010 Sophie Germain (p)
4648621027630345·2253824-1 76424 x242009 Sophie Germain (p)
5620366307356565·2253824-1 76424 x242009 Sophie Germain (p)
699064503957·2200008-1 60220 L952016 Sophie Germain (p)
7607095·2176311-1 53081 L9832009 Sophie Germain (p)
848047305725·2172403-1 51910 L992007 Sophie Germain (p)
9137211941292195·2171960-1 51780 x242006 Sophie Germain (p)
1021195711·2143630-1 43245 L34942019 Sophie Germain (p)

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

[up]   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: 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.

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