Factorial prime

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 their absence sometimes signals the end or the beginning of a lengthy run of consecutive composite numbers. For example, the prime following 6227020777 is 6227020867.

External links

• Mathworld entry for factorial primes

See also: Factorial prime, 23 (number), 2 (number), 3 (number), 5 (number), 7 (number), Composite number, Factorial, Mathematics