Here is another fact for those crazy about numbers. For some values of n, n!+1 is prime. For instance 3! + 1= 1x2x3 +1=7 is a prime. For other values of n, n! -1 is prime. For instance 4!-1= 1x2x3x4 -1=23 is prime. Numbers with one of these properties are known as factorial primes. Here are, as far as I know, the five largest known factorial primes: 34790! -1 (it has 142,891 digits) 26951! +1 (it has 107,707 digits) 21480! -1 (it has 83,727 digits) 6917! -1 (it has 23,560 digits) 6380! +1 (it has 21,507 digits)
Posted on: Fri, 17 Jan 2014 01:01:11 +0000
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