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Old 2004-02-25, 10:28   #6
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Jan 2004

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Default Factorial primes

Originally Posted by eepiccolo
Well, you have to look at all numbers <= to N!+1 to try to find a factor, not just numbers <=N.
Ex) 4! + 1 = 2*3*4 + 1 = 25, and 5 divides 25.

In fact, I'm not even sure if a prime number exists of the form N! + 1 for N >= 4.

However, in reference to the other part of your post, a 10M digit prime does not need to be a Mersenne prime to qualify for the prize.

EDIT: 11! + 1 is prime, but who knows if there are a finite numbers of primes in this form or not? (I'm sure someone knows.)
See Wilsons Theorem and Corollary on link
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