Factorials
In mathematics, the factorial of a natural number n is the product of the positive integers less than or equal to n. This is written as n! and pronounced n factorial’. The numeric value of n! can be calculated by repeated multiplication, if n is not too large. The Fundamental Counting Principle says that the number of ways to choose n items is n!
n! = n × (n— 1) × (n—2) × ……. × 3 × 2 × 1
Factorial Notation is used when you need to work with a series of factors, each being one less than the previous factor.
The factorial symbol “!” (an exclamation point) simply means the product of decreasing positive whole numbers.
For example, 4! = 4 × 3 × 2 × 1 = 24
Always remember that 0! = 1.