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 A109107 a(n) = (1/sqrt(26))((5+sqrt(26))^(n+1)-(5-sqrt(26))^(n+1)). 0
 2, 20, 202, 2040, 20602, 208060, 2101202, 21220080, 214302002, 2164240100, 21856703002, 220731270120, 2229169404202, 22512425312140, 227353422525602, 2296046650568160, 23187819928207202, 234174245932640180 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(n) = 2*A041041(n). 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. 284, K{Q(n)}). LINKS Tanya Khovanova, Recursive Sequences Index entries for linear recurrences with constant coefficients, signature (10, 1). FORMULA G.f.: 2/(1-10z-z^2). MAPLE a:=n->(1/sqrt(26))*((5+sqrt(26))^(n+1)-(5-sqrt(26))^(n+1)): seq(expand(a(n)), n=0..20); CROSSREFS Cf. A041041. Sequence in context: A093136 A037519 A037722 * A037729 A037624 A077327 Adjacent sequences:  A109104 A109105 A109106 * A109108 A109109 A109110 KEYWORD nonn AUTHOR Emeric Deutsch, Jun 19 2005 STATUS approved

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Last modified December 12 00:07 EST 2018. Contains 318052 sequences. (Running on oeis4.)