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 A108645 a(n) = (n+1)(n+2)^2*(n+3)^2*(n+4)(2n^2 + 6n + 5)/720. 1
 1, 26, 250, 1435, 5978, 19992, 56952, 143550, 328515, 695266, 1379378, 2591953, 4650100, 8015840, 13344864, 21546684, 33857829, 51929850, 77934010, 114684647, 165783310, 235785880, 330395000, 456680250, 623328615, 840927906, 1122285906 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS KekulĂ© numbers for certain benzenoids. REFERENCES S. J. Cyvin and I. Gutman, KekulĂ© structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (p. 230, no. 21). LINKS Harvey P. Dale, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (9, -36, 84, -126, 126, -84, 36, -9, 1). FORMULA G.f.: (-5*x^4-37*x^3-52*x^2-17*x-1)/(x-1)^9. - Harvey P. Dale, Sep 05 2016 MAPLE a:=(n+1)*(n+2)^2*(n+3)^2*(n+4)*(2*n^2+6*n+5)/720: seq(a(n), n=0..30); MATHEMATICA Table[(n+1)(n+2)^2(n+3)^2(n+4)(2n^2+6n+5)/720, {n, 0, 30}] (* or *) LinearRecurrence[{9, -36, 84, -126, 126, -84, 36, -9, 1}, {1, 26, 250, 1435, 5978, 19992, 56952, 143550, 328515}, 30] (* Harvey P. Dale, Sep 05 2016 *) CROSSREFS Sequence in context: A184461 A088889 A060105 * A086023 A296539 A229715 Adjacent sequences:  A108642 A108643 A108644 * A108646 A108647 A108648 KEYWORD nonn AUTHOR Emeric Deutsch, Jun 13 2005 STATUS approved

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Last modified March 20 21:49 EDT 2019. Contains 321352 sequences. (Running on oeis4.)