That formula has an error. It should be 
my $log_nfact =
  $n * (log ($n) - 1) + 0.5 * (log(2*PI*$n + 1/3));

[download]
log(exp(-n)) = -n

-Mark

In reply to Re^2: Stirling Approx to N! for large Number? by kvale
in thread Stirling Approx to N! for large Number? by monkfan

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