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.