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A109114
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a(n)=5a(n-1)-3a(n-2), a(0)=1, a(1)=6.
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3
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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; internal format)
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OFFSET
| 0,2
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COMMENTS
| Kekule numbers for certain benzenoids.
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REFERENCES
| S. J. Cyvin and I. Gutman, Kekule structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (pp. 302, P_{11}).
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FORMULA
| a(n)=[(sqrt(13)+7)((5+sqrt(13))/2)^n+(sqrt(13)-7)((5-sqrt(13))/2)^n]/(2sqrt(13)) G.f.=(1+z)/(1-5z+3z^2).
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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);
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CROSSREFS
| Sequence in context: A130019 A196919 A049651 * A080619 A080620 A080627
Adjacent sequences: A109111 A109112 A109113 * A109115 A109116 A109117
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KEYWORD
| nonn
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AUTHOR
| Emeric Deutsch (deutsch(AT)duke.poly.edu), Jun 19 2005
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