0FACTORIAL
The product of n consecutive natural numbers (or positive integers) from 1 to n is called as the factorial ‘n’. Factorial n is denoted by n!. i.e.,
n! = 1 × 2 × 3 × 4 × 5 × 6 ... (n − 2) (n − 1) n
3! = 1 × 2 × 3 = 6
4! = 1 × 2 × 3 × 4 = 24
5! = 1 × 2 × 3 × 4 × 5 = 120
6! = 1 × 2 × 3 × 4 × 5 × 6 = 720
Note: 0! = 1 and 1! = 1
Properties
(i) n! is always an even number if n ≥ 2.
(ii) n! always ends with zero if n ≥ 5.
