The generalized gamma functions

In this paper, we introduce a way to generalize the Euler's gamma function as well as some related special functions. With a given polynomial in one variable $f(t)\ge 0$, we can associate a function, so-called "gamma function associated with $f$", defined by $\Gamma_f(s) := \int_0^\infty f^{s-1} e^{-t} dt$. This function has many features similar to the Euler's gamma function. We also present some initial results on the gamma-type functional equation for $\Gamma_f(s)$ in some special cases.