N-factorial

     n             actual            factrl(n) 
     1                    1                    1
     2                    2                    2
     3                    6                    6
     4                   24                   24
     5                  120                  120
     6                  720                  720
     7                 5040                 5040
     8                40320                40320
     9               362880               362880
    10              3628800              3628800
    11             39916800             39916800
    12            479001600            479001600
    13           6227020800           6227020800
    14         8.717829e+10         8.717829e+10 
    15         1.307675e+12         1.307674e+12 
    20         2.432904e+18         2.432902e+18 
    25         1.551122e+25         1.551121e+25 
    30         2.652528e+32         2.652529e+32