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A116720
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Number of permutations of length n which avoid the patterns 213, 1234, 4312.
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1
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1, 2, 5, 12, 25, 44, 69, 100, 137, 180, 229, 284, 345, 412, 485, 564, 649, 740, 837, 940, 1049, 1164, 1285, 1412, 1545, 1684, 1829, 1980, 2137, 2300, 2469, 2644, 2825, 3012, 3205, 3404, 3609, 3820, 4037, 4260, 4489, 4724, 4965, 5212, 5465, 5724, 5989, 6260
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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(2x^4+2x^3+2x^2-x+1)}/{(x-1)^3}
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MAPLE
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A116720 := proc(n) coeftayl(-x*(2*x^4+2*x^3+2*x^2-x+1)/(x-1)^3, x=0, n) ; end: seq(A116720(n), n=1..60) ; # R. J. Mathar, Jan 23 2008
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MATHEMATICA
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LinearRecurrence[{3, -3, 1}, {1, 2, 5, 12, 25}, 50] (* Harvey P. Dale, May 06 2017 *)
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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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EXTENSIONS
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STATUS
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approved
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