Large Prime Number Found by SGI/Cray Supercomputer


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     A Large Prime Number: 2^1257787-1 
     A Large Perfect Number: 2^1257786 * (2^1257787-1) 
     The discovery team: David Slowinski: left, CRAY T94: center :-) & Paul Gage:
     right 
     San Jose Mercury News Article 


EAGAN, Minn., September 3, 1996 -- Computer scientists at SGI's Cray Research unit have
discovered a large prime number while conducting tests on a CRAY T90 series supercomputer. 

The prime number has 378,632 digits. Printed in newspaper-sized type, the number would fill
approximately 12 newspaper pages. 

In mathematical notation, the new prime number is expressed as 2^1257787-1 , which denotes
two, multiplied by itself 1,257,787 times, minus one. Numbers expressed in this form are called
Mersenne prime numbers after Father Marin Mersenne, a 17th century French monk who spent
years searching for prime numbers of this type. See Chris Callwell's prime page for more
information on prime numbers. 




Prime numbers can be divided evenly only by themselves and one. Examples include 2, 3, 5, 7, 11
and so on. The Greek mathematician Euclid proved that there are an infinite number of prime
numbers. But these numbers do not occur in a regular sequence and there is no formula for
generating them. Therefore, the discovery of new primes requires randomly generating and testing
millions of numbers. 

Silicon Graphics employees have been at the leading edge for prime number discoveries since
1978. The 10 of the last 11 records for the largest known prime belong to people who are now
working at Silicon Graphics: 

Prime            Digits  Year  SGI Employee

2^21701-1          6533  1978  Landon Curt Noll
                               (with Laura Nickel)
2^23209-1          6987  1979  Landon Curt Noll
2^44497-1         13395  1979  David Slowinski
                               (with Harry Nelson)
2^86243-1         25962  1982  David Slowinski
2^132049-1        39751  1983  David Slowinski
2^216091-1        65050  1985  David Slowinski
391581 *          65087  1989  Landon Curt Noll
   2^216193-1                  John Brown
                               Sergio Zarantonello
                               (with Joel & Gene Smith, Bodo Parady)
2^756839-1       227832  1992  David Slowinski
                               Paul Gage
2^859433-1       258716  1994  David Slowinski
                               Paul Gage
2^1257787-1      378632  1996  David Slowinski
                               Paul Gage

"Finding these special numbers is a true 'needle-in-a-haystack' exercise, but we improve our odds
by using a tremendously fast computer and a clever program," said David Slowinski, a Cray
Research computer scientist. and fellow Cray Research computer scientist Paul Gage developed
the program that found the this large prime number. Mathematician Richard Crandall (of NeXT),
independently verified that the number Slowinski and Gage found is prime.