Factorial

The factorial of a positive integer, n, denoted "n!", is the product of the positive integers less than or equal to n. e.g.

: 5! = 5 * 4 * 3 * 2 * 1 = 120

: 10! = 10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 *1 = 3628800

It is possible to define factorial for numbers other than positive integers, but to do so requires the use of the gamma function.