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A109114 a(n) = 5*a(n-1) - 3*a(n-2), a(0)=1, a(1)=6. 3
1, 6, 27, 117, 504, 2169, 9333, 40158, 172791, 743481, 3199032, 13764717, 59226489, 254838294, 1096512003, 4718045133, 20300689656, 87349312881, 375844495437, 1617174538542, 6958339206399, 29940172416369, 128825844462648 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Kekulé numbers for certain benzenoids.

REFERENCES

S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (p. 302, P_{11}).

LINKS

Table of n, a(n) for n=0..22.

Index entries for linear recurrences with constant coefficients, signature (5,-3).

FORMULA

a(n) = ((sqrt(13) + 7)*((5 + sqrt(13))/2)^n + (sqrt(13) - 7)*((5 - sqrt(13))/2)^n)/(2*sqrt(13)).

G.f.: (1+z)/(1 - 5z + 3z^2).

MAPLE

a[0]:=1: a[1]:=6: for n from 2 to 26 do a[n]:=5*a[n-1]-3*a[n-2] od: seq(a[n], n=0..26);

MATHEMATICA

LinearRecurrence[{5, -3}, {1, 6}, 30] (* Harvey P. Dale, Dec 03 2012 *)

CROSSREFS

Sequence in context: A130019 A196919 A049651 * A080619 A265943 A080620

Adjacent sequences:  A109111 A109112 A109113 * A109115 A109116 A109117

KEYWORD

nonn

AUTHOR

Emeric Deutsch, Jun 19 2005

STATUS

approved

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Last modified September 24 11:06 EDT 2020. Contains 337317 sequences. (Running on oeis4.)