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A098995
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Number of permutations of [n] with exactly 4 descents which avoid the pattern 1324.
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1
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0, 0, 0, 0, 1, 57, 812, 6524, 37309, 169298, 648216, 2176923, 6582869, 18262399, 47129249, 114344261, 262987603, 577216181, 1215552037, 2467076907, 4843870146, 9229556242, 17113017451, 30949065535, 54705281270, 94677736245, 160689668475, 267828562140, 438931138500
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OFFSET
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1,6
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LINKS
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Index entries for linear recurrences with constant coefficients, signature (17,-136,680,-2380,6188,-12376,19448,-24310,24310,-19448,12376,-6188,2380,-680,136,-17,1).
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FORMULA
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G.f.: x^5*(1 + 40*x - 21*x^2 - 208*x^3 + 453*x^4 - 379*x^5 + 74*x^6 + 107*x^7 - 92*x^8 + 30*x^9 - 4*x^10) / (1 - x)^17.
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PROG
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(PARI) concat(vector(4), Vec(x^5*(1 + 40*x - 21*x^2 - 208*x^3 + 453*x^4 - 379*x^5 + 74*x^6 + 107*x^7 - 92*x^8 + 30*x^9 - 4*x^10) / (1 - x)^17 + O(x^30))) \\ Colin Barker, Nov 03 2017
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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