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 A114480 Kekulé numbers for certain benzenoids. 0
 4, 50, 650, 8500, 111250, 1456250, 19062500, 249531250, 3266406250, 42757812500, 559707031250, 7326660156250, 95907226562500, 1255441894531250, 16433947753906250, 215123168945312500, 2815998840332031250 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (p. 205). LINKS Index entries for linear recurrences with constant coefficients, signature (15,-25). FORMULA a(n) = 2*((sqrt(5) + 2)((15 + 5*sqrt(5))/2)^(n-1) + (sqrt(5) - 2)*((15 - 5*sqrt(5))/2)^(n-1))/sqrt(5). From Colin Barker, Aug 30 2013: (Start) a(n) = 15*a(n-1) - 25*a(n-2). G.f.: -2*x*(5*x-2) / (25*x^2 - 15*x + 1). (End) MAPLE a:=2*((sqrt(5)+2)*((15+5*sqrt(5))/2)^(n-1)+(sqrt(5)-2)*((15-5*sqrt(5))/2)^(n-1))/sqrt(5): seq(expand(a(n)), n=1..20); CROSSREFS Sequence in context: A232731 A215792 A280358 * A123356 A234870 A139087 Adjacent sequences:  A114477 A114478 A114479 * A114481 A114482 A114483 KEYWORD nonn AUTHOR Emeric Deutsch, Nov 30 2005 STATUS approved

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Last modified February 24 07:45 EST 2020. Contains 332199 sequences. (Running on oeis4.)