factorial


1fac·to·ri·al

adjective \fak-ˈtr-ē-əl\

Definition of FACTORIAL

:  of, relating to, or being a factor or a factorial

First Known Use of FACTORIAL

1837

2factorial

noun

Definition of FACTORIAL

1
:  the product of all the positive integers from 1 to n —symbol n!
2
:  the quantity 0! arbitrarily defined as equal to 1

First Known Use of FACTORIAL

1869

factorial

noun    (Concise Encyclopedia)

For any whole number, the product of all the counting numbers up to and including itself. It is indicated with an exclamation point: 4! (read “four factorial”) is 1 2 3 4 = 24. In order for certain formulas involving permutations and combinations to work, 0! is defined to be 1. Factorials are particularly useful in calculating the number of ways an event can occur, for example, the number of possible orders of finish in a race.

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