An approximation for $n$ !, when $n$ is large, is given by
$$
n ! \approx \sqrt{2 n \pi}\left(\frac{n}{e}\right)^n\left(1+\frac{1}{12 n-1}\right)
$$
Calculate 12 !, 20 !, and 25 ! on your calculator. Then use Stirling's formula to approximate 12 !, 20 !, and 25 !.