A116846 - OEIS

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A116846

Number of permutations of length n which avoid the patterns 321, 12354.

1, 1, 2, 5, 14, 41, 113, 277, 607, 1212, 2245, 3913, 6488, 10319, 15845, 23609, 34273, 48634, 67641, 92413, 124258, 164693, 215465, 278573, 356291, 451192, 566173, 704481, 869740, 1065979, 1297661, 1569713, 1887557, 2257142, 2684977, 3178165, 3744438, 4392193

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OFFSET

0,3

LINKS

Table of n, a(n) for n=0..37.

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.: 1+x(x^8-4x^7+3x^6+6x^5-13x^4+14x^3-12x^2+5x-1)/(x-1)^7.

For n >= 3, a(n) = (n^6 + 9n^5 - 5n^4 - 405n^3 + 1804n^2 - 684n - 2160)/720. - Franklin T. Adams-Watters, Sep 16 2006

CROSSREFS

Sequence in context: A243881 A358416 A225691 * A080558 A116844 A116851

Adjacent sequences: A116843 A116844 A116845 * A116847 A116848 A116849

KEYWORD

nonn,easy

AUTHOR

Lara Pudwell, Feb 26 2006

STATUS

approved