What is the "!" for?

!. This is called "factorial function", which means this: 5!=5 x 4 x 3 x 2 x 1 =120

basically ur multiplying that number and times the number below it and below that number.

ex. 4! = 4*3*2*1 which also equals 24 

5! = 5*4*3*2*1 which also equals 120