# Factorial of a non-integer number

My TI-83 calculator doesnt allow me to do this, but using Windows calculator, I can compute the factorial of say 5.8. What does this mean and how does it work?

-
 As I recall, these calculators can compute factorials of half-integers. But yes, you need $\Gamma(z)$ in general. – J. M. Nov 28 '10 at 1:29