Molly C. answered • 11/17/17

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There are two types of factorial primes: factorials plus one (n!+1) and factorials minus one (n! -1)

• n!+1 is prime for n=1, 2, 3, 11, 27, 37, 41, 73, 77, 116, 154, 320, 340, 399, 427, 872, 1477, 6380, and 26951 (107707 digits)

So, n might be prime, but it is not always prime.