This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A109107 #9 Mar 16 2017 14:36:31
%S A109107 2,20,202,2040,20602,208060,2101202,21220080,214302002,2164240100,
%T A109107 21856703002,220731270120,2229169404202,22512425312140,
%U A109107 227353422525602,2296046650568160,23187819928207202,234174245932640180
%N A109107 a(n) = (1/sqrt(26))((5+sqrt(26))^(n+1)-(5-sqrt(26))^(n+1)).
%C A109107 a(n) = 2*A041041(n). Kekulé numbers for certain benzenoids.
%D A109107 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)}).
%H A109107 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>
%H A109107 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (10, 1).
%F A109107 G.f.: 2/(1-10z-z^2).
%p A109107 a:=n->(1/sqrt(26))*((5+sqrt(26))^(n+1)-(5-sqrt(26))^(n+1)): seq(expand(a(n)),n=0..20);
%Y A109107 Cf. A041041.
%K A109107 nonn
%O A109107 0,1
%A A109107 _Emeric Deutsch_, Jun 19 2005