Factorial of an integer n (written as n! and read as "n factorial") is simply a product of the number "n" and all natural numbers smaller than n. That is,
n! = n × (n-1) × (n-2) × … × 3 × 2 × 1
Note : Remember that factorial of 0 is 1. (0! = 1)
Factorials are most commonly used in "Permutations and Combinations", a branch of Mathematics usually studied under "Probability". However, other areas of mathematics use factorials as well.
Permutations and Combinations are represented by following expression :
Where both m, n are integers.
Factorials grow exponentially. It is said that in some cases, the growth of factorials is faster than that of exponentials.