**Factorial**

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!. Press **MENU 1**
to access the RUN-MAT menu. Press **6**. We now need to paste the factorial
symbol after the 6. Press **OPTN** to see the MAT menu options, press **F6**
to see more options, press **F1** to select PROB to access the probability
menu, and press **1** to select **1: x**