English

Counting alternating permutations with restricted prefix and suffix

Combinatorics 2025-02-18 v1

Abstract

In this paper, we use Hasse diagrams and generating functions to count alternating permutations with restricted prefix and suffix of lengths 3 and 4. In other words, for an alternating permutation σ=σ1σ2σ3σnSn\sigma=\sigma_1\sigma_2\sigma_3\cdots\sigma_{n}\in S_{n}, we restrict length-3 prefixes σ1σ2σ3\sigma_1\sigma_2\sigma_3 to follow certain patterns, such as 231231 and 132132, or follow certain restrictions such as σ2max{σ1,σ3}+2\sigma_2 \geq \max\{\sigma_1,\sigma_3\}+2, similarly for prefixes of length 4. We also study the enumeration of alternating permutations with restrictions on both prefix and suffix.

Keywords

Cite

@article{arxiv.2502.10727,
  title  = {Counting alternating permutations with restricted prefix and suffix},
  author = {Ran Pan and Jeffrey Remmel},
  journal= {arXiv preprint arXiv:2502.10727},
  year   = {2025}
}
R2 v1 2026-06-28T21:45:21.148Z