Welcome to the factorial world :) Remember the Exclamation Point ( ! ) on the calculator, that is called factorial.
For instance: 1! = 1
2! = 1 x 2
3! = 1 x 2 x 3
and so on
10! = 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x 10 = 3628800
Crazy enough, 0! is actually equal to 1, try that on your calculator XD
