Factorial Factorial of a whole number 'n' is defined as the product of that number with every whole number till 1. Formula for n Factorial: n! = n * (n - 1) * (n - 2) * ...... * 1 1! = 1 2! = 2 * 1 = 2 3! = 3 * 2 * 1 = 6 4! = 4 * 3 * 2 * 1 = 24 Installation npm i factorial-of-numbers