English

Consecutive patterns in restricted permutations and involutions

Combinatorics 2023-06-22 v3

Abstract

It is well-known that the set In\mathbf I_n of involutions of the symmetric group Sn\mathbf S_n corresponds bijectively - by the Foata map FF - to the set of nn-permutations that avoid the two vincular patterns 123,\underline{123}, 132.\underline{132}. We consider a bijection Γ\Gamma from the set Sn\mathbf S_n to the set of histoires de Laguerre, namely, bicolored Motzkin paths with labelled steps, and study its properties when restricted to Sn(123,132).\mathbf S_n(1\underline{23},1\underline{32}). In particular, we show that the set Sn(123,132)\mathbf S_n(\underline{123},{132}) of permutations that avoids the consecutive pattern 123\underline{123} and the classical pattern 132132 corresponds via Γ\Gamma to the set of Motzkin paths, while its image under FF is the set of restricted involutions In(3412).\mathbf I_n(3412). We exploit these results to determine the joint distribution of the statistics des and inv over Sn(123,132)\mathbf S_n(\underline{123},{132}) and over In(3412).\mathbf I_n(3412). Moreover, we determine the distribution in these two sets of every consecutive pattern of length three. To this aim, we use a modified version of the well-known Goulden-Jacson cluster method.

Keywords

Cite

@article{arxiv.1902.02213,
  title  = {Consecutive patterns in restricted permutations and involutions},
  author = {M. Barnabei and F. Bonetti and N. Castronuovo and M. Silimbani},
  journal= {arXiv preprint arXiv:1902.02213},
  year   = {2023}
}

Comments

24 pages

R2 v1 2026-06-23T07:33:39.672Z