Factorial

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Definition

Factorial is the result of multiplying a sequence of descending natural numbers (such as 4 × 3 × 2 × 1)

The Factorial symbol is "!".

factorial symbol

4! is usually pronounced "4 factorial", but some people even say "4 shriek" or "4 bang".

Example

4! = 4 × 3 × 2 × 1 = 24
7! = 7 × 6 × 5 × 4 × 3 × 2 × 1 = 5040
1! = 1

Calculating From the Previous Value

We can easily calculate a factorial from the previous one:

n n!    
1 1 1 1
2 2 × 1 = 2 × 1! = 2
3 3 × 2 × 1 = 3 × 2! = 6
4 4 × 3 × 2 × 1 = 4 × 3! = 24
5 5 × 4 × 3 × 2 × 1 = 5 × 4! = 120
6 etc. etc. etc.

Reference & Resources

  • http://www.mathsisfun.com/numbers/factorial.html

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