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A116766
Number of permutations of length n which avoid the patterns 2134, 3421, 4312.
0
1, 2, 6, 21, 71, 200, 465, 929, 1667, 2766, 4325, 6455, 9279, 12932, 17561, 23325, 30395, 38954, 49197, 61331, 75575, 92160, 111329, 133337, 158451, 186950, 219125, 255279, 295727, 340796
OFFSET
1,2
FORMULA
G.f.: -((6x^8-7x^7-7x^6+4x^5+11x^4+x^3+6x^2-3x+1)*x)/(x-1)^5.
For n >= 5, a(n) = (n^4 - 5n^3 + 9n^2 - 57n + 202)/2. - Franklin T. Adams-Watters, Sep 16 2006
MATHEMATICA
(1 - 3x + 6x^2 + x^3 + 11x^4 + 4x^5 - 7x^6 - 7x^7 + 6x^8)/(1 - x)^5 + O[x]^30 // CoefficientList[#, x]& (* Jean-François Alcover, May 06 2017 *)
CROSSREFS
Sequence in context: A116794 A294719 A116795 * A116825 A116767 A116759
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved