the factorial of 0 is 1
the factorial of 1 is 1
the factorial of 2 is 2
the factorial of 3 is 6
the factorial of 4 is 24
the factorial of 5 is 120
the factorial of 6 is 720
the factorial of 7 is 5040
the factorial of 8 is 40320
the factorial of 9 is 362880