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 A305270 #15 Feb 12 2021 12:00:29 %S A305270 28,168,448,1008,2128,4368,8848,17808,35728,71568,143248,286608, %T A305270 573328,1146768,2293648,4587408,9174928,18349968,36700048,73400208, %U A305270 146800528,293601168,587202448,1174405008,2348810128,4697620368,9395240848,18790481808,37580963728,75161927568,150323855248 %N A305270 a(n) = 140*2^n - 112. %C A305270 a(n) is the number of edges in the polyphenylene dendrimer G[n], defined pictorially in the Arif et al. reference (see Fig. 1, where G[2] is shown). %H A305270 Colin Barker, <a href="/A305270/b305270.txt">Table of n, a(n) for n = 0..1000</a> %H A305270 N. E. Arif, Roslan Hasni and Saeid Alikhani, <a href="http://dx.doi.org/10.3923/jas.2012.2279.2282">Fourth order and fourth sum connectivity indices of polyphenylene dendrimers</a>, J. Applied Science, 12 (21), 2012, 2279-2282. %H A305270 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2). %F A305270 From _Colin Barker_, May 31 2018: (Start) %F A305270 G.f.: 28*(1 + 3*x) / ((1 - x)*(1 - 2*x)). %F A305270 a(n) = 3*a(n-1) - 2*a(n-2) for n>1. %F A305270 (End) %p A305270 seq(140*2^n-112, n = 0..40); %o A305270 (PARI) Vec(28*(1 + 3*x) / ((1 - x)*(1 - 2*x)) + O(x^40)) \\ _Colin Barker_, May 31 2018 %Y A305270 Cf. A305269, A305271, A305272. %K A305270 nonn,easy %O A305270 0,1 %A A305270 _Emeric Deutsch_, May 30 2018