The factorial of $n \in \N$, written $n!$, is defined recursively:
- \[0! = 1.\]
For all $n \in \N^+$,
\[n! = (n - 1)! \cdot n.\]
Note.βFor $n \in \N^+$ we have
\[n! = \prod_{k = 1}^n k.\]The factorial of $n \in \N$, written $n!$, is defined recursively:
- \[0! = 1.\]
For all $n \in \N^+$,
\[n! = (n - 1)! \cdot n.\]
Note.βFor $n \in \N^+$ we have
\[n! = \prod_{k = 1}^n k.\]