On the inversion of $y^\alpha e^y$ in terms of associated Stirling numbers

Abstract

The function $y=\Phi_\alpha(x)$, the solution of $y^\alpha e^y=x$ for $x$ and $y$ large enough, has a series expansion in terms of $\ln x$ and $\ln\ln x$, with coefficients given in terms of Stirling cycle numbers. It is shown that this expansion converges for $x>(\alpha e)^\alpha$ for $\alpha \ge 1$. It is also shown that new expansions can be obtained for $\Phi_\alpha$ in terms of associated Stirling numbers. The new expansions converge more rapidly and on a larger domain.