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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

Table of n, a(n) for n=0..33.

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.)