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A116746
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Number of permutations of length n which avoid the patterns 1243, 4123, 4213.
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0
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1, 2, 6, 21, 75, 262, 890, 2949, 9575, 30590, 96486, 301269, 933171, 2872102, 8794946, 26822901, 81539855, 247232702, 748061070, 2259653349, 6816525435, 20540701510, 61842968906, 186063857829, 559486534391, 1681592864702
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OFFSET
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1,2
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LINKS
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FORMULA
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G.f.: A(x) = -{(4x^4+5x^3-12x^2+6x-1)x}/{(x-1)(3x-1)(2x-1)(x^2+2x-1)}
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MATHEMATICA
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LinearRecurrence[{8, -22, 22, -1, -6}, {1, 2, 6, 21, 75}, 40] (* Harvey P. Dale, Jul 25 2018 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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