Typically you wouldn't use lgamma to compute exact values of factorials at all. For a real world example of this function in action, look at John D. Cook's blog

Typically you wouldn't use lgamma to compute exact values of factorials at all. For a real world example of this function in action, look at John D. Cook's blog: [1]: http://www.johndcook.com/blog/2012/07/14/log-gamma-differences/ http://www.johndcook.com/blog/2012/07/14/log-gamma-differenc... [2]: http://www.johndcook.com/blog/2010/08/16/how-to-compute-log-factorial/ http://www.johndcook.com/blog/2010/08/16/how-to-compute-log-... [3]: http://www.johndcook.com/blog/2008/04/24/how-to-calculate-binomial-probabilities/ http://www.johndcook.com/blog/2008/04/24/how-to-calculate-bi...