MathGloss/F/Factorial

Factorial
the factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n.

Examples
1) 3! = 3x2x1=6

2) 4!=4x3x2x1 =24

3) 5! =5x4x3x2x1=120

4) 2! = 2x1 =2

5) 1! = 1

6) 0! = 1