Meaning & use
factorial
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The product of all positive integers from 1 up to a given number, written as that number followed by an exclamation point.
See it in a sentence
The factorial of 5, written 5!, equals 120.
Factorials grow extremely quickly, which is why they're used to count possible arrangements.
A note on using this word
By definition, the factorial of 0 is 1, a common point of confusion for students first learning the concept.
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