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.