# Factorial Operator

The factorial operator is represented using the (exclamation mark) symbol. The operator is unary, meaning that it only operates on one expression. For example, the factorial of the number is shown below.

The operator is used when calculating combinations and permutations.

## Usage

The factorial operator is used when calculating combinations and permutations. It is found in the formulas below:

The number of permutations of n distinct items is given by n factorial. A permutation is a unique ordering or arangment of the set of items.

The combination formula describes the possible combinations of r elements out of a group of n elements where order does not matter.

The permutation formula describes the possible permutations of r elements out of a group of n elements where order does matter.