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A109108
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a(n)=10a(n-1)+a(n-2), a(0)=1,a(1)=9.
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0
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1, 9, 91, 919, 9281, 93729, 946571, 9559439, 96540961, 974969049, 9846231451, 99437283559, 1004219067041, 10141627953969, 102420498606731, 1034346614021279, 10445886638819521, 105493213002216489
(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 (p.284, K{Q_1(n)}).
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LINKS
| Tanya Khovanova, Recursive Sequences
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FORMULA
| a(n)=(1/2/sqrt(26))((sqrt(26)+4)(5+sqrt(26))^n+(sqrt(26)-4)(5-sqrt(26))^n). G.f.=(1-z)/(1-10z-z^2)
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MAPLE
| a:=n->(1/2/sqrt(26))*((sqrt(26)+4)*(5+sqrt(26))^n+(sqrt(26)-4)*(5-sqrt(26))^n): seq(expand(a(n)), n=0..20);
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CROSSREFS
| Sequence in context: A020243 A014992 A015585 * A163456 A176735 A123792
Adjacent sequences: A109105 A109106 A109107 * A109109 A109110 A109111
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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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