## FANDOM

77 Pages

The factorial function of natural numbers is a function that takes a natural number and returns the product of all nonzero naturals less than or equal to that number. For example, $3! = 3 \times 2 \times 1 = 6$.

It can be expressed in product notation as $\prod_{n=1}^{x} n$, or in the form of a recurrence relation as $n! = n \left( n - 1 \right)!$.

$0!$ is equal to one because it is the empty product.