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Pattern-restricted permutations composed of 3-cycles
Affiliation:University of Texas at Tyler, Tyler, TX 75799, USA
Abstract:In this paper, we characterize and enumerate pattern-avoiding permutations composed of only 3-cycles. In particular, we answer the question for the six patterns of length 3. We find that the number of permutations composed of n 3-cycles that avoid the pattern 231 (equivalently 312) is given by 3n?1, while the generating function for the number of those that avoid the pattern 132 (equivalently 213) is given by a formula involving the generating functions for the well-known Motzkin numbers and Catalan numbers. The number of permutations composed of n 3-cycles that avoid the pattern 321 is characterized by a weighted sum involving statistics on Dyck paths of semilength n.
Keywords:Pattern avoidance  Cycles  Dyck paths  Motzkin numbers  Catalan numbers
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