# What is 1! - Factorial for integer 1?

## Definition & Formula

**Factorial** is a basic mathematic function often represented by **n!** in mathematics, represents the product of all integers less than or equal to the positive integer n. An important function frequently used in combinatorics (*permutations* & *combinations*) theory.

For example, 1! can be written as

1! = 1

1! = 1