A116762 Number of permutations of length n which avoid the patterns 1234, 1243, 3421.

1, 2, 6, 21, 73, 223, 587, 1356, 2820, 5395, 9653, 16355, 26487, 41299, 62347, 91538, 131178, 184023, 253333, 342929, 457253, 601431, 781339, 1003672, 1276016, 1606923, 2005989, 2483935, 3052691, 3725483

Offset

1,2

Links

Table of n, a(n) for n=1..30.

D. Callan, T. Mansour, Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns, arXiv:1705.00933 (2017), Table 2 No 61.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).

Formula

G.f.: A(x) = {x(x^9-4x^8+3x^7+x^6+8x^5-17x^4+14x^3-13x^2+5x-1)}/{(x-1)^7}

For n >= 5, a(n) = (27n^5 - 450n^4 + 4045n^3 - 21450n^2 + 62228n - 74880)/120. - Franklin T. Adams-Watters, Sep 16 2006

Crossrefs

Sequence in context: A294759 A294760 A116834 * A116803 A116829 A116824

Adjacent sequences: A116759 A116760 A116761 * A116763 A116764 A116765

Keyword

nonn,easy

Author

Lara Pudwell, Feb 26 2006

Status

approved