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 A054275 #24 Sep 08 2022 08:45:00
%S A054275 1,8,24,52,90,140,200,272,354,448,552,668,794,932,1080,1240,1410,1592,
%T A054275 1784,1988,2202,2428,2664,2912,3170,3440,3720,4012,4314,4628,4952,
%U A054275 5288,5634,5992,6360,6740,7130,7532,7944,8368,8802,9248,9704,10172,10650,11140
%N A054275 Susceptibility series H_2 for 2-dimensional Ising model (divided by 2).
%H A054275 Colin Barker, <a href="/A054275/b054275.txt">Table of n, a(n) for n = 0..1000</a>
%H A054275 A. J. Guttmann, <a href="https://doi.org/10.1016/S0012-365X(99)00262-9">Indicators of solvability for lattice models</a>, Discrete Math., 217 (2000), 167-189.
%H A054275 D. Hansel et al., <a href="http://dx.doi.org/10.1007/BF01010400">Analytical properties of the anisotropic cubic Ising model</a>, J. Stat. Phys., 48 (1987), 69-80.
%H A054275 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1).
%F A054275 G.f.: (1+6*x+8*x^2+6*x^3+x^4) / ((1-x)^3*(1+x)).
%F A054275 From _Colin Barker_, Dec 09 2016: (Start)
%F A054275 a(n) = (11*n^2+4)/2 for n>0 and even.
%F A054275 a(n) = (11*n^2+5)/2 for n odd.
%F A054275 a(n) = 2*a(n-1) - 2*a(n-3) + a(n-4) for n>4. (End)
%F A054275 E.g.f.: ((9 + 22*x + 22*x^2)*exp(x) - 4 - exp(-x))/4. - _G. C. Greubel_, Jul 31 2019
%t A054275 CoefficientList[Series[(1+6*x+8*x^2+6*x^3+x^4)/((1-x)^3*(1+x)),{x,0,50}], x] (* or *) LinearRecurrence[{2,0,-2,1},{1,8,24,52,90},51] (* _Indranil Ghosh_, Feb 24 2017 *)
%t A054275 Table[If[n==0, 1, (22*n^2+9-(-1)^n)/4], {n,0,50}] (* _G. C. Greubel_, Jul 31 2019 *)
%o A054275 (PARI) Vec((1+6*x+8*x^2+6*x^3+x^4)/((1-x)^3*(1+x)) + O(x^50)) \\ _Colin Barker_, Dec 09 2016
%o A054275 (PARI) a(n)=if(n, 11*n^2+5, 2)\2 \\ _Charles R Greathouse IV_, Feb 24 2017
%o A054275 (Magma) [n eq 0 select 1 else (22*n^2+9-(-1)^n)/4: n in [0..50]]; // _G. C. Greubel_, Jul 31 2019
%o A054275 (Sage) [1]+[(22*n^2+9-(-1)^n)/4 for n in (1..50)] # _G. C. Greubel_, Jul 31 2019
%o A054275 (GAP) Concatenation([1], List([1..50], n-> (22*n^2+9-(-1)^n)/4)); # _G. C. Greubel_, Jul 31 2019
%Y A054275 Cf. A008574, A054410, A054389, A054764.
%K A054275 nonn,easy
%O A054275 0,2
%A A054275 _N. J. A. Sloane_, May 09 2000