Factorial is a quantity defined for all non-negative integers. Note that zero is an integer which is neither positive nor negative.
If 'n' is an integer greater than or equal to zero, the factorial of 'n' is the product of all positive integers less than or equal to n.
It is denoted commonly by n! and occasionally by
. It is read as "factorial n".
We shall use the exclamation symbol (!) hereafter.
The factorial of zero i.e., 0! is defined as 1.
Factorial of negative integers and fractions is not defined.
Example:
3! = 3 × 2 × 1 = 6
6! = 6 × 5 × 4 × 3 × 2 × 1 = 720
10! = 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1 = 36,28,800
As 'n' increases the value of n! increases very fast. See adjacent table.