Restricted signed permutations counted by the Schröder numbers |
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Authors: | Eric S. Egge |
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Affiliation: | Department of Mathematics and Computer Science, Carleton College, Northfield, MN 55057, USA |
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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. |
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Keywords: | Restricted permutation Pattern-avoiding permutation Forbidden subsequence Schrö der number Signed permutation Generating tree |
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