English

Enumeration on polyominoes determined by Catalan words avoiding $(\geq,\geq)$

Combinatorics 2025-04-08 v1

Abstract

A Catalan word of length nn that avoids the pattern (,)(\geq, \geq) is a sequence w=w1wnw=w_1\cdots w_n with w1=0w_1=0 and 0wiwi1+10\leq w_i\leq w_{i-1}+1 for all ii, while ensuring that no subsequence satisfies wiwi+1wi+2w_i \geq w_{i+1}\geq w_{i+2} for i=2,,ni=2,\ldots,n. These words are enumerated by the nn-th Motzkin number. From such a word, we associate a nn-column Motzkin polyomino (called a (,)(\geq,\geq)-polyomino), where the ii-th column contains wi+1w_i+1 bottom-aligned cells. In this paper, we derive generating functions for (,)(\geq,\geq)-polyominoes based on their length, area, semiperimeter, last symbol value, and number of interior points. We provide asymptotic analyses and closed-form expressions for the total area, total semiperimeter, sum of the last symbol values, and total number of interior points across all (,)(\geq,\geq)-polyominoes of a given length. Finally, we express all these results as linear combinations of trinomial coefficients.

Cite

@article{arxiv.2504.04828,
  title  = {Enumeration on polyominoes determined by Catalan words avoiding $(\geq,\geq)$},
  author = {M. Ahmia and J. -L. Baril and B. Rezig},
  journal= {arXiv preprint arXiv:2504.04828},
  year   = {2025}
}
R2 v1 2026-06-28T22:49:04.180Z