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 A116842 Number of permutations of length n which avoid the patterns 1234, 2143, 3421. 0
 1, 2, 6, 21, 69, 181, 375, 651, 1009, 1449, 1971, 2575, 3261, 4029, 4879, 5811, 6825, 7921, 9099, 10359, 11701, 13125, 14631, 16219, 17889, 19641, 21475, 23391, 25389, 27469 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS D. Callan, T. Mansour, Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns, arXiv:1705.00933 (2017), Table 2 No 3. Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005. Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA G.f.: A(x) = -{x(18x^6+31x^5+22x^4+8x^3+3x^2-x+1)}/(x-1)^3. FOr n >= 5, a(n) = 41n^2 - 339n + 739. - Franklin T. Adams-Watters, Sep 16 2006 MAPLE cn := [1, -2, 2, 2, 8, 22, 31, 18] ; p := add(cn[i]*x^(i-1), i=1..nops(cn)) ; q := (1-x)^3 ; taylor(p/q, x=0, 40) ; gfun[seriestolist](%) ; # R. J. Mathar, Nov 07 2017 CROSSREFS Sequence in context: A119098 A294706 A294707 * A294708 A294709 A116774 Adjacent sequences:  A116839 A116840 A116841 * A116843 A116844 A116845 KEYWORD nonn,easy AUTHOR Lara Pudwell, Feb 26 2006 STATUS approved

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Last modified September 26 16:43 EDT 2020. Contains 337374 sequences. (Running on oeis4.)