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 A308750 Number of Dumont permutations of the first kind of length 2n avoiding pattern 2143 (or pattern 3421). 0
 1, 1, 2, 7, 36, 239, 1892, 17015, 168503, 1799272, 20409644 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Conjecture: The number of Dumont permutations of the first kind avoiding pattern 2143 equals the number of Dumont permutations of the first kind avoiding pattern 3421 for all n >= 0. Data for n=7,8,9,10 is due to Michael Albert. REFERENCES O. Jones, Enumeration of Dumont permutations avoiding certain four-letter patterns, Ph.D. thesis, Howard University, 2019. LINKS D. Dumont, Interprétations combinatoires des nombres de Genocchi, Duke Math. J., 41 (1974), 305-318. EXAMPLE For n=3, the 7 Dumont permutations of the first kind avoiding pattern 2143 are 356421, 364215, 435621, 563421, 564213, 634215, 642135, and the 7 Dumont permutations of the first kind avoiding pattern 3421 are 214365, 216435, 421365, 421563, 421635, 621435, 642135. CROSSREFS Cf. A001469, A110501. Sequence in context: A019030 A212411 A119736 * A088715 A088313 A201197 Adjacent sequences:  A308747 A308748 A308749 * A308751 A308752 A308753 KEYWORD nonn,more AUTHOR Alexander Burstein and Opel Jones, Jun 21 2019 STATUS approved

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Last modified May 27 02:42 EDT 2020. Contains 334647 sequences. (Running on oeis4.)