- This article was written long time ago. For more accurate article, refer to article 30 - $\gamma(z)$ can be defined like this. (1) $\Gamma(z)=(z-1)!=\gamma(z)+m, m$: integer. $\gamma(z)=(z-1)!-m$ The reason that $m$ is added is to divide into integer part and $\gamma(z)$ whose real part is less than $1$. Using the relation $z-n=(-1)^{n+1}\cos^{n+1}\frac{\pi (z-n+1)}{2((z-n)!+1)}$, wh..