Some properties of a class of refined Eulerian polynomials

Abstract

In recent, H. Sun defined a new kind of refined Eulerian polynomials, namely, \begin{eqnarray*} A_n(p,q)=\sum_{π\in \mathfrak{S}_n}p^{{\rm odes}(π)}q^{{\rm edes}(π)} \end{eqnarray*} for $n\ge 1$, where $odes(\pi )$ and $edes(\pi )$ enumerate the number of descents of permutation $\pi$ in odd and even positions, respectively. In this paper, we build an exponential generating function for $A_n(p,q)$ and establish an explicit formula for $A_n(p,q)$ in terms of Eulerian polynomials $A_n(q)$ and $C(q)$, the generating function for Catalan numbers. In certain special case, we set up a connection between $A_n(p,q)$ and $A_n(p,0)$ or $A_n(0,q)$, and express the coefficients of $A_n(0,q)$ by Eulerian numbers. Specially, this connection creates a new relation between Euler numbers and Eulerian numbers.

10 pages