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Restricted signed permutations counted by the Schröder numbers
Authors:Eric S. Egge
Affiliation:Department of Mathematics and Computer Science, Carleton College, Northfield, MN 55057, USA
Abstract:Gire, West, and Kremer have found ten classes of restricted permutations counted by the large Schröder numbers, no two of which are trivially Wilf-equivalent. In this paper we enumerate eleven classes of restricted signed permutations counted by the large Schröder numbers, no two of which are trivially Wilf-equivalent. We obtain five of these enumerations by elementary methods, five by displaying isomorphisms with the classical Schröder generating tree, and one by giving an isomorphism with a new Schröder generating tree. When combined with a result of Egge and a computer search, this completes the classification of restricted signed permutations counted by the large Schröder numbers in which the set of restrictions consists of two patterns of length 2 and two of length 3.
Keywords:Restricted permutation   Pattern-avoiding permutation   Forbidden subsequence   Schrö  der number   Signed permutation   Generating tree
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