(統計) $\Gamma (Gamma)函數$

 $$\Gamma(n)=(n-1)!$$

$$\Gamma(z)=\displaystyle\int_0^{\infty}t^{z-1}e^{-t}\ dt \ \ \ \  \Re(z)>0$$

EX:

$\displaystyle\int_0^{\infty} x^2e^{-x}dx=\Gamma(3)=2$