Factorial, permutations, combinations

$\displaystyle 4! = 1 \times 2 \times 3 \times 4$, as the slide shows. Check it: 2nd F and 4 is the factorial. Type 4, press , , and : 24.. 2nd F and 6 counts permutations. Type 10, press , , type 3, and press : 720.. 2nd F and 5 counts combinations. Type 5, press , , type 2, and press : 10..

▶ Watch this step in the video (23:20)