**Learning Objective:**

**What is Factorial?****What is n x (n - 1)!**

**Concept:**

**The product of 'n' natural numbers is called factorial.****For example if we multiply first 5 natural numbers, we obtain 5 factorial and if we multiply first 10 natural numbers, we obtain 10 factorial.****Factorial is denoted as "!". So the product of n natural numbers is n! (read as n factorial).**

**For example 1 x 2 x 3 .....n = n!****For example (Reverse Order) n x (n-1) x (n-2) ..... x 3 x 2 x 1 = n!****For example 1 x 2 x 3 x 4 x 5 = 5!****For example (Reverse Order) 5 x 4 x 3 x 2 x 1 = 5!****For example 1 x 2 x 3 x 4 x 5 x 6 = 6!****For example (Reverse Order) 6 x 5 x 4 x 3 x 2 x 1 = 6!**