Factorial, permutations, combinations

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