Factorial

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

The symbol is "!"

Examples:

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