Q. What is Factorial?
A factorial is a number with a factorial sign, !, after it.
5! is read "five factorial."
3! is read "three factorial."
The factorial of a natural number is the product of that number and all the whole numbers less than it, stopping at 1. In general,
n! = n.(n-1).......2.1
For completeness, 0! is defined to be 1.
The number of permutations equals the factorial of the number of objects.