my question is simple : if $a_n$ and $z_n$ are both real positive sequences tending to $+\infty$, what is the asymptotic ($n \to +\infty$) behaviour of $\Gamma(a_n,z_n)$ when 1) $a_n \neq z_n$ and $\frac{a_n}{z_n} \to 1$ and 2) $a_n << z_n$ ?
Thanks :)