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 A277990 #39 Sep 08 2022 08:46:17
%S A277990 0,60,228,504,888,1380,1980,2688,3504,4428,5460,6600,7848,9204,10668,
%T A277990 12240,13920,15708,17604,19608,21720,23940,26268,28704,31248,33900,
%U A277990 36660,39528,42504,45588,48780,52080,55488,59004,62628,66360,70200,74148,78204,82368,86640
%N A277990 a(n) = 54*n^2 + 6*n.
%C A277990 For n > 0, a(n) is the first Zagreb index of the polycyclic aromatic hydrocarbon PAH[n]. The first Zagreb index of a simple connected graph is the sum of the squared degrees of its vertices. Alternately, it is the sum of the degree sums d(i)+ d(j) over all edges ij of the graph. The pictorial definition of PAH[n] can be viewed in the Farahani reference.
%C A277990 The M-polynomial of the polycyclic aromatic hydrocarbon PAH[n] is M(PAH[n], x, y) = 6*n*x*y^3 + 3*n*(3*n-1)*x^3*y^3.
%C A277990 Also sequence found by reading the line from 0, in the direction 0, 60, ..., in the square spiral whose vertices are the generalized 29-gonal numbers (A303815). - _Omar E. Pol_, Nov 12 2016
%H A277990 E. Deutsch and Sandi Klavzar, <a href="http://dx.doi.org/10.22052/ijmc.2015.10106">M-polynomial and degree-based topological indices</a>, Iranian J. Math. Chemistry, 6, No. 2, 2015, 93-102.
%H A277990 M. R. Farahani, <a href="http://www.jchemacta.com/index.php/amc/article/view/99">Some connectivity indices of polycyclic aromatic hydrocarbons (PAHs)</a>, Advances in Materials and Corrosion, 1, 2013, 65-69.
%H A277990 I. Gutman and K. C. Das, <a href="http://match.pmf.kg.ac.rs/electronic_versions/Match50/match50_83-92.pdf">The first Zagreb index 30 years after</a>, MATCH Commun. Math. Comput. Chem. 50, 2004, 83-92.
%H A277990 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A277990 G.f.: 12*x*(5 + 4*x)/(1 - x)^3.
%F A277990 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). - _Vincenzo Librandi_, Nov 13 2016
%p A277990 seq(54*n^2+6*n, n = 1..45);
%t A277990 Table[54n^2+6n,{n,0,40}] (* or *) LinearRecurrence[{3,-3,1},{0,60,228},50] (* _Harvey P. Dale_, Jan 28 2020 *)
%o A277990 (Magma) [54*n^2+6*n: n in [0..40]]; // _Vincenzo Librandi_, Nov 13 2016
%o A277990 (PARI) a(n)=54*n^2+6*n \\ _Charles R Greathouse IV_, Jun 17 2017
%Y A277990 Cf. A277991, A303815.
%K A277990 nonn,easy
%O A277990 0,2
%A A277990 _Emeric Deutsch_, Nov 12 2016