Catalan words avoiding a pattern of length four
DOI:
https://doi.org/10.55016/g3gszf44Abstract
Let $\mathcal{C}_n$ denote the set of Catalan words of length $n$ and $\mathcal{C}_n(p)$ the subset of $\mathcal{C}_n$ whose members avoid the pattern $p$. In this paper, we enumerate members of $\mathcal{C}_n(p)$ where $p$ is a permutation pattern of length four. This extends recent work on Catalan words concerning the avoidance of classical, consecutive or vincular patterns of length at most three. Indeed, we determine the generating function of the distribution for the number of descents on each of the corresponding avoidance classes. We make use of the symbolic counting method to establish our results, together with a variety of other enumerative techniques, including use of strategic decompositions, introduction of auxiliary generating functions and analysis of active sites.
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Copyright (c) 2026 Jean-Luc Baril, Toufik Mansour, Jose L. Ramirez, Mark Shattuck

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