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arXiv · 1008.2375

A bijection to count (1-23-4)-avoiding permutations

David Callan
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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.

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David Callan. 2010-08-13. A bijection to count (1-23-4)-avoiding permutations. https://arxiv.org/abs/1008.2375

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