Two new triangles of $q$-integers via $q$-Eulerian polynomials of type $A$ and $B$

Abstract

The classical Eulerian polynomials can be expanded in the basis $t^{k-1}(1+t{)}^{n+1-2k}$ ($1\le k\le \lfloor (n+1)/2\rfloor$) with positive integral coefficients. This formula implies both the symmetry and the unimodality of the Eulerian polynomials. In this paper, we prove a $q$-analogue of this expansion for Carlitz's $q$-Eulerian polynomials as well as a similar formula for Chow-Gessel's $q$-Eulerian polynomials of type $B$. We shall give some applications of these two formulae, which involve two new sequences of polynomials in the variable $q$ with positive integral coefficients. An open problem is to give a combinatorial interpretation for these polynomials.

13 pages, to appear in The Ramanujan Journal