log of n_factorial

     n              actual             factln(n)
     1            0.0000000            0.0000000
     2            0.6931472            0.6931472
     3            1.7917595            1.7917595
     4            3.1780538            3.1780539
     5            4.7874917            4.7874918
     6            6.5792512            6.5792513
     7            8.5251614            8.5251617
     8           10.6046029           10.6046028
     9           12.8018275           12.8018274
    10           15.1044126           15.1044130
    11           17.5023078           17.5023079
    12           19.9872145           19.9872150
    13           22.5521639           22.5521641
    14           25.1912212           25.1912212
    15           27.8992722           27.8992710
    20           42.3356174           42.3356171
    25           58.0036060           58.0036049
    30           74.6582362           74.6582336