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A165533
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Number of permutations of length n which avoid the patterns 4213 and 1432.
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1
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1, 1, 2, 6, 22, 87, 352, 1434, 5861, 24019, 98677, 406291, 1676009, 6924618, 28646875, 118638038, 491765865, 2039944740, 8467475533, 35166107745, 146115418937, 607353499821, 2525443862594, 10504254304765, 43702642447260, 181865873468907, 756979080521743, 3151341504417932
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OFFSET
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0,3
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LINKS
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FORMULA
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G.f.: 1 + x*(1 - x)*(1 - 2*x)*(1 - 7*x + 17*x^2 - 16*x^3 + 4*x^4 + (1 - 3*x + 3*x^2)*sqrt(1 - 4*x))/(2 - 22*x + 96*x^2 - 220*x^3 + 282*x^4 - 196*x^5 + 64*x^6 - 8*x^7). - G. C. Greubel, Oct 22 2018
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EXAMPLE
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There are 22 permutations of length 4 which avoid these two patterns, so a(4)=22.
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MATHEMATICA
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CoefficientList[Series[1 + x*(1 - x)*(1 - 2*x)*(1 - 7*x + 17*x^2 - 16*x^3 + 4*x^4 + (1 - 3*x + 3*x^2)*Sqrt[1 - 4*x])/(2 - 22*x + 96*x^2 - 220*x^3 + 282*x^4 - 196*x^5 + 64*x^6 - 8*x^7), {x, 0, 50}], x] (* G. C. Greubel, Oct 22 2018 *)
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PROG
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(PARI) x='x+O('x^50); Vec(1 + x*(1-x)*(1-2*x)*(1-7*x+17*x^2-16*x^3+4*x^4 + (1-3*x+3*x^2)*sqrt(1-4*x))/(2-22*x+96*x^2-220*x^3+282*x^4-196*x^5 + 64*x^6-8*x^7)) \\ G. C. Greubel, Oct 22 2018
(Magma) m:=50; R<x>:=PowerSeriesRing(Rationals(), m); Coefficients(R!(1 + x*(1-x)*(1-2*x)*(1-7*x+17*x^2-16*x^3+4*x^4 +(1-3*x + 3*x^2)*Sqrt(1 - 4*x))/(2-22*x+96*x^2-220*x^3+282*x^4-196*x^5+64*x^6-8*x^7))); // G. C. Greubel, Oct 22 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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