The number n! is formally defined by the recursive formula

**0! = 1
(n + 1)! = (n + 1) x n!**

This quantity is frequently thought as **n! = n x (n - 1) x (n - 2) x ... x 2 x 1.**

For example, we compute 6!. From the home screen, first type .
We then paste the factorial symbol after the 6.
Factorial is found in the MATH menu, Probability submenu. Press ** MATH**
(located above the 5 key). Then press to select 7: Probability.
Press either or to select 1: !.
After 6! is
displayed in the entry line, press . Hence, 6! = 720.