# Factorials

Factorials are products of positive integers.

The value " $n$ factorial ", written $n!$ , for a whole number $n$ is the product of all the whole numbers from $1$ to $n$ .

$n!=1×2×...×\left(n-2\right)×\left(n-1\right)×n$

For example, $5!$ is equal to $120$ :

$5!=1×2×3×4×5=120$

(For various reasons, $0!$ is defined to be equal to $1$ , not $0$ .)