Factorial prime
From Wikipedia, the free encyclopedia.

A factorial prime is a number that is one less or one more than a factorial and is also a prime number. The first few factorial primes are

2, 3, 5, 7, 23, 719, 5039, 39916801, 479001599, 87178291199

Factorial primes are of interest to number theorists because they sometimes signal the end or the beginning of an extraordinarily lengthy run of consecutive composite numbers.

Reference

The definition given at http://mathworld.wolfram.com/FactorialPrime.html, from Wolfram Research, the makers of Mathematica 4.

The original article can be found at: http://en.wikipedia.org/wiki/Factorial_prime.
All text is available under the terms of the GNU Free Documentation License.