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 A194646 Number of ways to place 4n nonattacking kings on an 8 X 2n cylindrical chessboard. 4
 80, 276, 1082, 4460, 18890, 81606, 358564, 1599820, 7238864, 33175486, 153802520, 720390254, 3404944506, 16221905696, 77820675992, 375564803020, 1821845982082, 8876847931644, 43416046650306, 213033152875350, 1048198981050148, 5169676077206180 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This cylinder is horizontal: a chessboard where it is supposed that rows 1 and 2n are in contact (number of columns = 8, number of rows = 2n). LINKS FORMULA a(n) = 4 + 2*5^n + 2*4^n + 2*(2+sqrt(3))^n+2*(2-sqrt(3))^n + 4*((5+sqrt(5))/2)^n+4*((5-sqrt(5))/2)^n + 4*((5+sqrt(13))/2)^n+4*((5-sqrt(13))/2)^n + 2*(2*cos(Pi/7))^(2n)+2*(2*cos(2*Pi/7))^(2n)+2*(2*cos(3*Pi/7))^(2n). Recurrence: a(n) = -300*a(n-12) + 4235*a(n-11) - 23320*a(n-10) + 66422*a(n-9) - 111545*a(n-8) + 118727*a(n-7) - 83449*a(n-6) + 39539*a(n-5) - 12676*a(n-4) + 2708*a(n-3) - 369*a(n-2) + 29*a(n-1). G.f.: -2*(-17 + 453*x - 5251*x^2 + 34737*x^3 - 144635*x^4 + 394423*x^5 - 711101*x^6 + 836705*x^7 - 620007*x^8 + 270365*x^9 - 61055*x^10 + 5335*x^11)/((-1+x)*(-1+4*x)*(-1+5*x)*(1-4*x+x^2)*(1-5*x+3*x^2)*(1-5*x+5*x^2)*(-1+5*x-6*x^2+x^3)). MATHEMATICA Table[FullSimplify[4+2*5^n+2*4^n + 2*(2+Sqrt[3])^n + 2*(2-Sqrt[3])^n+ 4*((5+Sqrt[5])/2)^n + 4*((5-Sqrt[5])/2)^n + 4*((5+Sqrt[13])/2)^n+4*((5-Sqrt[13])/2)^n+ 2*(2*Cos[Pi/7])^(2n) + 2*(2*Cos[2*Pi/7])^(2n) + 2*(2*Cos[3*Pi/7])^(2n)], {n, 10}] CROSSREFS Cf. A173782, A194644, A194645, A137432, A195592. Sequence in context: A234890 A157912 A234883 * A057441 A204483 A204475 Adjacent sequences:  A194643 A194644 A194645 * A194647 A194648 A194649 KEYWORD nonn AUTHOR Vaclav Kotesovec, Aug 31 2011 STATUS approved

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Last modified November 29 07:48 EST 2021. Contains 349416 sequences. (Running on oeis4.)