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 A121254 #8 Aug 09 2015 12:00:54 %S A121254 4,16,60,208,680,2136,6524,19520,57492,167240,481624,1375536 %N A121254 Number of conjugated cycles composed of six carbons in (n,n)-nanotubes in terms of the number of naphthalene units. %C A121254 See Table 2 on page 412 of Lukovits and Janezic paper for details. %H A121254 I. Lukovits et al. <a href="http://dx.doi.org/10.1021/ci034240k">Enumeration of conjugated circuits in nanotubes</a>, J. Chem. Inf. Comput. Sci. 44 (2004), 410-414. %H A121254 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (6, -11, 6, -1). %F A121254 Conjecture: a(n)=6a(n-1)-11a(n-2)+6a(n-3)-a(n-4)=4*A117202(n). G.f.: 4*x*(1-2*x+2*x^2)/(x^2-3*x+1)^2. [From _R. J. Mathar_, Mar 18 2009] %e A121254 If n=5 then the number of conjugated cycles composed of six carbons in (n,n)-nanotubes is 680 which is the fifth term in the sequence. Here n is the number of naphthalene units. %K A121254 nonn %O A121254 1,1 %A A121254 _Parthasarathy Nambi_, Aug 22 2006