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A165538
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Number of permutations of length n which avoid the patterns 4312 and 3142.
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3
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1, 2, 6, 22, 88, 367, 1568, 6810, 29943, 132958, 595227, 2683373, 12170778, 55499358, 254297805, 1170248190, 5406570910, 25068420955, 116617923611, 544157590706, 2546278167018, 11945937322413, 56180864428301
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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. f satisfies: (x^3-2*x^2+x)*f^4+(4*x^3-9*x^2+6*x-1)*f^3+(6*x^3-12*x^2+7*x-1)*f^2+(4*x^3-5*x^2+x)*f+x^3 = 0.
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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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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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