I don't get it!!!

! In math means factorial.

 

When talking about integers, it means multiply all the positive integers that appear before it.

 

For example: 2! = 2*1

3! = 3*2*1 = 6

4! = 4*3*2*1 = 24

5! = 5*4*3*2*1 = 120

and so on.

 

It's used in combinatorics and probablility. It's also a way to tell how amny possible ways there are to arrange n number of objects.

 

I hope this helps!