What is a subfactorial and how to solve it?

What is a subfactorial and how to solve it? #shorts #shortsviral

[JacksonDavis-mf]

Explanation for fun:

For 4!, you do 4 x 3 x 2 x 1 which is 24
(4 x 3 = 12, 12 x 2 = 24, and 24 x 1 = 24).
So for 4! we have 24 combinations.

Write out 1, 2, 3, 4 in 24 combinations.

b a c d
b c d a

B is in its same place twice so cross out those series of numbers that have the repeating places the letter's set on.

At some point, you get 9 combinations or 9