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A116840
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Number of permutations of length n which avoid the patterns 1234, 1243, 2431.
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0
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1, 2, 6, 21, 75, 256, 826, 2535, 7474, 21370, 59718, 164082, 445266, 1197326, 3198035, 8499466, 22505676, 59427975, 156598649, 412008060, 1082704623, 2842662437, 7458393801, 19558738331, 51270256195, 134356895501
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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.: (x^8 -6x^7 +17x^6 -40x^5 +58x^4 -52x^3 +28x^2 -8x+1)*x/((2x-1) (x^2-3x+1)(x-1)^5)
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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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