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 A109113 a(n) = 6a(n-1) + 3a(n-2), a(0)=2, a(1)=14. 0
 2, 14, 90, 582, 3762, 24318, 157194, 1016118, 6568290, 42458094, 274453434, 1774094886, 11467929618, 74129862366, 479182963050, 3097487365398, 20022473081538, 129427300585422, 836631222757146, 5408069238299142 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 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. 302, P_{15}). LINKS Index entries for linear recurrences with constant coefficients, signature (6,3). FORMULA a(n) = ((3 + 2sqrt(3))^(n+1) + (3 - 2sqrt(3))^(n+1))/3. G.f.: 2(1+z)/(1 - 6z - 3z^2). a(n) = 2*abs(A099842(n)). - F. Chapoton, May 06 2014 MAPLE a[0]:=2: a[1]:=14: for n from 2 to 25 do a[n]:=6*a[n-1]+3*a[n-2] od: seq(a[n], n=0..22); PROG (PARI) Vec((14+6*x)/(1-6*x-3*x^2)+O(x^99)) \\ Charles R Greathouse IV, May 06 2014 CROSSREFS Sequence in context: A065892 A139183 A174705 * A081959 A002464 A282051 Adjacent sequences:  A109110 A109111 A109112 * A109114 A109115 A109116 KEYWORD nonn,easy AUTHOR Emeric Deutsch, Jun 19 2005 STATUS approved

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Last modified December 16 19:11 EST 2018. Contains 318188 sequences. (Running on oeis4.)