# FactorialΒΆ

*Factorial*, written `!`

, is a unary operator
written after its argument, defined as the product of all the natural
numbers from 1 up to \(n\), that is, \(n! = 1 \times 2
\times 3 \times \dots \times n\).

```
Disco> :doc !
~! : β β β
n! computes the factorial of n, that is, 1 * 2 * ... * n.
https://disco-lang.readthedocs.io/en/latest/reference/factorial.html
Disco> 3!
6
Disco> 4!
24
Disco> 4! == 1 * 2 * 3 * 4
true
Disco> (4!)!
620448401733239439360000
Disco> ((4!)!)!
Error: that number would not even fit in the universe!
Disco> 0!
1
```

Note that \(0! = 1\) by definition, since a product of zero things should be the identity value for multiplication.