A bijection to count (1-23-4)-avoiding permutations
Combinatorics
2010-08-16 v1
Abstract
A permutation is (1-23-4)-avoiding if it contains no four entries, increasing left to right, with the middle two adjacent in the permutation. Here we give a 2-variable recurrence for the number of such permutations, improving on the previously known 4-variable recurrence. At the heart of the proof is a bijection from (1-23-4)-avoiding permutations to increasing ordered trees whose leaves, taken in preorder, are also increasing.
Cite
@article{arxiv.1008.2375,
title = {A bijection to count (1-23-4)-avoiding permutations},
author = {David Callan},
journal= {arXiv preprint arXiv:1008.2375},
year = {2010}
}
Comments
latex, 16 pages