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 !. Finally, press EXE. Hence, 6! = 720.