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A116809
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Number of permutations of length n which avoid the patterns 1432, 2134, 2143.
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1
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1, 2, 6, 21, 76, 273, 971, 3439, 12172, 43098, 152649, 540730, 1915445, 6785029, 24034177, 85134498, 301565746, 1068215101, 3783864272, 13403320805, 47477655647, 168176809999, 595721056436, 2110181402286, 7474749309041
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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) = -{(x-1)^4x}/{x^5-5x^4+13x^3-12x^2+6x-1}
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MAPLE
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f:= gfun:-rectoproc({a(n)-5*a(n+1)+13*a(n+2)-12*a(n+3)+6*a(n+4)-a(n+5), a(0) = 0, a(1) = 1, a(2) = 2, a(3) = 6, a(4) = 21, a(5) = 76}, a(n), remember):
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MATHEMATICA
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LinearRecurrence[{6, -12, 13, -5, 1}, {1, 2, 6, 21, 76}, 25] (* Jean-François Alcover, Sep 19 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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