Remixed Eulerian numbers

Philippe Nadeau (1, 2, 3) , Vasu Tewari (4)

1 CTN - Combinatoire, théorie des nombres
2 ICJ - Institut Camille Jordan
3 CNRS - Centre National de la Recherche Scientifique
4 UHM - University of Hawai‘i [Mānoa]

Remixed Eulerian numbers are a polynomial $q$-deformation of Postnikov's mixed Eulerian numbers. They arose naturally in previous work by the authors concerning the permutahedral variety and subsume well-known families of polynomials such as $q$-binomial coefficients and Garsia--Remmel's $q$-hit numbers. We study their combinatorics in more depth. As polynomials in $q$, they are shown to be symmetric and unimodal. By interpreting them as computing success probabilities in a simple probabilistic process we arrive at a combinatorial interpretation involving weighted trees. By decomposing the permutahedron into certain combinatorial cubes, we obtain a second combinatorial interpretation. At $q=1$, the former recovers Postnikov's interpretation whereas the latter recovers Liu's interpretation, both of which were obtained via methods different from ours.

Domaines: Combinatoire [math.CO]

Philippe Nadeau, Vasu Tewari. Remixed Eulerian numbers. Forum of Mathematics, Sigma, 2023, 11 (e65), ⟨10.1017/fms.2023.57⟩. ⟨hal-03747973⟩