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A109112
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a(n)=6a(n-1)-3a(n-2), a(0)=2, a(1)=13.
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0
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2, 13, 72, 393, 2142, 11673, 63612, 346653, 1889082, 10294533, 56099952, 305716113, 1665996822, 9078832593, 49475005092, 269613532773, 1469256181362, 8006696489853, 43632410395032, 237774372900633, 1295749006218702
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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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 (p.302, P_{14}).
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FORMULA
| a(n)=[1/2sqrt(6)][(2sqrt(6)+7)(3+sqrt(6))^n+(2sqrt(6)-7)(3-sqrt(6))^n] G.f.=(2+z)/(1-6z+3z^2)
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MAPLE
| a[0]:=2:a[1]:=13: for n from 2 to 24 do a[n]:=6*a[n-1]-3*a[n-2] od: seq(a[n], n=0..24);
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CROSSREFS
| Sequence in context: A128743 A188676 A097349 * A163190 A004027 A154357
Adjacent sequences: A109109 A109110 A109111 * A109113 A109114 A109115
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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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