Some two-sided inequalities for multiple Gamma functions and related results

摘要

There is an abundant literature on inequalities for the (Euler’s) Gamma function Γ and its various related functions. Yet, only very recently, several authors began to study inequalities for the (Barnes’) double Gamma function Γ2. Here, in this paper, we aim at presenting several two-sided inequalities for the multiple Gamma functions Γn (n=2,3,4,5). In our investigation of these two-sided inequalities for the multiple Gamma functions Γn (n=2,3,4,5), we employ and extend a method based upon Taylor’s formula and express logΓn(1+x) as series involving the Zeta functions. We also give a more convenient explicit form of the multiple Gamma functions Γn (n∈N),N being the set of positive integers. The main two-sided inequalities for the multiple Gamma functions Γn (n=2,3,4,5) (which we have presented in this paper) are presumably new and their derivations provide a fruitful insight into the corresponding problem for the multiple Gamma functions Γn when n≧6.