A109107 a(n) = (1/sqrt(26))((5+sqrt(26))^(n+1)-(5-sqrt(26))^(n+1)).

2, 20, 202, 2040, 20602, 208060, 2101202, 21220080, 214302002, 2164240100, 21856703002, 220731270120, 2229169404202, 22512425312140, 227353422525602, 2296046650568160, 23187819928207202, 234174245932640180

Offset: 0

Author

Emeric Deutsch, Jun 19 2005

Keywords

• nonn

Comments

a(n) = 2*A041041(n). 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. 284, K{Q(n)}).

Links

• Tanya Khovanova, Recursive Sequences
• Index entries for linear recurrences with constant coefficients, signature (10, 1).

Crossrefs

Cf. A041041.

Programs

Maple

a:=n->(1/sqrt(26))*((5+sqrt(26))^(n+1)-(5-sqrt(26))^(n+1)): seq(expand(a(n)),n=0..20);

Formula

G.f.: 2/(1-10z-z^2).