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 A277980 #35 Sep 08 2022 08:46:17
%S A277980 0,30,84,162,264,390,540,714,912,1134,1380,1650,1944,2262,2604,2970,
%T A277980 3360,3774,4212,4674,5160,5670,6204,6762,7344,7950,8580,9234,9912,
%U A277980 10614,11340,12090,12864,13662,14484,15330,16200,17094,18012,18954,19920
%N A277980 a(n) = 12*n^2 + 18*n.
%C A277980 For n>=3, a(n) is the second Zagreb index of the double-wheel graph DW[n]. The second Zagreb index of a simple connected graph g is the sum of the degree products d(i) d(j) over all edges ij of g.
%C A277980 The double-wheel graph DW[n] consists of two cycles C[n], whose vertices are connected to an additional vertex.
%C A277980 The M-polynomial of the double-wheel graph DW[n] is M(DW[n],x,y) = 2*n*x^3*y^3 + 2*n*x^3*y^{2*n}.
%H A277980 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 A277980 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A277980 G.f.: 6*x*(5-x)/(1-x)^3.
%F A277980 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3).
%F A277980 a(n) = 6*A014106(n).
%F A277980 a(n) = A152746(n+1) - 6 = A154105(n) - 7. - _Omar E. Pol_, May 08 2018
%e A277980 a(3) = 162. Indeed, the double-wheel graph DW[3] has 6 edges with end-point degrees 3,3 and 6 edges with end-point degrees 3,6. Then the second Zagreb index is 6*9 + 6*18 = 162.
%p A277980 seq(12*n^2+18*n, n = 0 .. 50);
%t A277980 Table[12 n^2 + 18 n, {n, 0, 45}] (* _Vincenzo Librandi_, Nov 09 2016 *)
%o A277980 (Magma) [12*n^2+18*n: n in [0..40]]; // _Vincenzo Librandi_, Nov 09 2016
%o A277980 (PARI) a(n)=12*n^2+18*n \\ _Charles R Greathouse IV_, Nov 09 2016
%Y A277980 Cf. A014106, A152746, A154105, A277979.
%Y A277980 First bisection of A277978.
%Y A277980 After 0, subsequence of A255265.
%K A277980 nonn,easy
%O A277980 0,2
%A A277980 _Emeric Deutsch_, Nov 08 2016