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A200316
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Number of permutations of [1..n] that can be drawn on a circle.
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0
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1, 2, 6, 22, 84, 308, 1090, 3782, 13000, 44504, 152102, 519506, 1773948, 6056932, 20680010, 70606382, 241065744, 823050480, 2810070734, 9594182314, 32756588164, 111837988444, 381838777906, 1303679135238, 4451038985688, 15196797672872, 51885112720758, 177146855537986
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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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Vatter and Waton give a g.f.
G.f.: x*(2*x^5-4*x^4+5*x^3-9*x^2+5*x-1) / ((x-1)^3*(2*x^2-4*x+1)). - Colin Barker, Jul 05 2013
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MATHEMATICA
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Rest[CoefficientList[Series[x (2x^5-4x^4+5x^3-9x^2+5x-1)/((x-1)^3 (2x^2- 4x+ 1)), {x, 0, 30}], x]] (* Harvey P. Dale, Sep 29 2013 *)
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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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