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 A122658 a(n) = if n mod 2 = 1 then n^3*(n-1)^2/2 else n^5/2. 1
 0, 0, 16, 54, 512, 1000, 3888, 6174, 16384, 23328, 50000, 66550, 124416, 158184, 268912, 330750, 524288, 628864, 944784, 1111158, 1600000, 1852200, 2576816, 2944414, 3981312, 4500000, 5940688, 6652854, 8605184, 9560488, 12150000, 13405950, 16777216, 18399744 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Szeged index of product of two cycles of length n. REFERENCES J. Zerovnik, Szeged index of symmetric graphs, J. Chem. Inf. Comput. Sci., 39 (1999), 77-80. LINKS Index entries for linear recurrences with constant coefficients, signature (1,5,-5,-10,10,10,-10,-5,5,1,-1). FORMULA a(n) = (n^3*(1-(-1)^n+2*(-1+(-1)^n)*n+2*n^2))/4. G.f.: 2*x^2*(x^8 +7*x^7 +95*x^6 +113*x^5 +379*x^4 +149*x^3 +189*x^2 +19*x +8) / ((x -1)^6*(x +1)^5). - Colin Barker, Sep 20 2013 MATHEMATICA Table[If[OddQ[n], n^3 (n-1)^2/2, n^5/2], {n, 0, 40}] (* or *) LinearRecurrence[ {1, 5, -5, -10, 10, 10, -10, -5, 5, 1, -1}, {0, 0, 16, 54, 512, 1000, 3888, 6174, 16384, 23328, 50000}, 40] (* Harvey P. Dale, Nov 20 2016 *) CROSSREFS Cf. A122656. Sequence in context: A167690 A297842 A172190 * A224040 A244805 A188838 Adjacent sequences:  A122655 A122656 A122657 * A122659 A122660 A122661 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Sep 22 2006 STATUS approved

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Last modified July 22 20:51 EDT 2019. Contains 325226 sequences. (Running on oeis4.)