What is meant by $n!$ in a mathematical expression?

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Answer 1 · 2014-10-18T16:45:32

Definition (Factorials)

$0! =1$

$n! =n cdot (n-1)cdot(n-2)cdotcdotscdot2cdot1$ for all natural number $n$ .

For example,

$5! = 5cdot4cdot3cdot2cdot1=120$

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What is meant by n!n! in a mathematical expression?