## Facts!

### Definition

For integers n ³ 0, n factorial (written n!) is defined by
• 0! = 1
• n! = (n) * (n-1) * (n-2) * ... * (3) * (2) * (1)

### Who created the factorial?

The factorial notation of n! was first used by Christian Kramp in 1808 as a convenience to the printer. Kramp also did work on relating the factorial to non-integers; usually, the factorial is used only with non-negative integers. To learn more about how certain mathematical symbols were introduced into the field, check out Jeff Miller's webpage on the subject.

### Interesting Factorial Facts

• 10! = 3,628,800, which is the number of seconds in six weeks!

• 11! is larger than the number of seconds in a year!

• 12! exceeds the number of seconds in 12 years!

• 13! surpasses the number of seconds in a century!

• n! is one of the fastest growing functions - it grows faster than any of the polynomial functions or the exponential functions!

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