Python factorial(x) function returns the x factorial. x should be an integer and greater than 0. It's a method of math module. x! = 1 * 2 * 3 * ... * (x-1) * x 0! = 1

>>> import math
>>> math.factorial(0) #0!

1

>>> math.factorial(1) #1!

1

>>> math.factorial(2) #2!

2

>>> math.factorial(3) #3!

6

>>> math.factorial(4) #4!

24

>>> math.factorial(5) #5!

120