Definition:Factorial/Historical Note

Definition
The symbol $!$ used on for the factorial, which is now universal, was introduced by  in his 1808 work Élémens d'arithmétique universelle.

Before that, various symbols were used whose existence is now of less importance.

Notations for $n!$ in history include the following:
 * $\left[{n}\right]$ as used by
 * $\mathop{\Pi} n$ as used by
 * $\left\lvert{\kern-2pt\underline n}\right.$ and $\left.{\underline n\kern-2pt}\right\rvert$, once popular in England and Italy.