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       0.8717829E+11       0.8717829E+11
    15       0.1307675E+13       0.1307674E+13
    20       0.2432904E+19       0.2432902E+19
    25       0.1551122E+26       0.1551121E+26
    30       0.2652528E+33       0.2652529E+33