(HP65) Factorial and Gamma Function

[Dieter]

(10-22-2017 08:49 AM)peacecalc Wrote:  which formula you use for your little program?

Since this has not been answered yet: it's Stirling's appproximation. The program uses the first terms of the series given in the section "Speed of convergence and error estimates". In my modified version the n² and n³ coefficents have been replaced by optimized values.

BTW I just realize that the linked Wikipedia article has some nice other approximations that may be worth a try, e.g. the one by Nemes (2007).

Dieter