- From: E Crane
- Date: 17 Feb 1999
*Subject: What does "!" mean?*
Dear Maths Help, I hope you do not mind me troubling you with a question. I am seventy-nine years old, and try to keep my mind active by doing mathematics problems and "surfing" the internet. My question is: what does the exclamation mark mean when it is written after a number? I came across it in the answer section to a book of mathematical puzzles. |

The exclamation mark symbol is pronounced "factorial" when used in mathematics.
It is shorthand for what you get when you multiply the given number (which must be a positive whole number) by
all the smaller whole numbers down to 1.

For example:

So you can see that factorials get quite big very quickly.

Two "special cases" are:

Factorials have several applications. The most common one is:

N different items can be placed in a row in N! different ways |

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