`!`

)`Factorial[`

`n`]`n`!- computes the factorial of
`n`.

`20!`

`Factorial`

handles numeric (real and complex) values using the gamma function:

`10.5!`

`(-3.0+1.5*I)!`

However, the value at poles is `ComplexInfinity`

:

`(-1.)!`

`Factorial`

has the same operator (`!`

) as `Not`

, but with higher precedence:

`!a! //FullForm`