A factorial has the form n! and is the product of the integer (n) and all the positive integers below it. For example, 5! = 5 x 4 x 3 x 2 x 1 = 120.
4! = ?
3 x 2 x 1
4 x 3
4 x 3 x 2 x 1
5 x 4 x 3 x 2 x 1