A116742 Number of permutations of length n which avoid the patterns 1342, 2341, 4132; or avoid the patterns 2431, 3124, 4231.

1, 2, 6, 21, 75, 261, 877, 2852, 9020, 27877, 84533, 252331, 743389, 2166062, 6252642, 17905365, 50922495, 143958513, 404848717, 1133309336, 3159610856, 8776920517, 24301859561, 67091484631, 184734559165, 507443649506

Offset

1,2

Links

Table of n, a(n) for n=1..26.

Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.

Index entries for linear recurrences with constant coefficients, signature (8,-23,28,-13,2)

Formula

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

Crossrefs

Sequence in context: A294771 A294814 A116816 * A116746 A116806 A116736

Adjacent sequences: A116739 A116740 A116741 * A116743 A116744 A116745

Keyword

nonn,easy

Author

Lara Pudwell, Feb 26 2006

Status

approved