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 A330357 #15 Apr 19 2023 16:53:45
%S A330357 2,3,4,7,10,15,20,27,34,43,52,63,74,87,100,115,130,147,164,183,202,
%T A330357 223,244,267,290,315,340,367,394,423,452,483,514,547,580,615,650,687,
%U A330357 724,763,802,843,884,927,970,1015,1060,1107,1154,1203,1252,1303,1354,1407
%N A330357 a(n) = (2*n^2 + 9 - (-1)^n)/4.
%H A330357 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1).
%F A330357 G.f.: (2 - x - 2*x^2 + 3*x^3)/(1 - 2*x + 2*x^3 - x^4) = (2 - x - 2*x^2 + 3*x^3)/((1 - x)^2 * (1 - x^2)).
%F A330357 a(n) = a(-n) for all n in Z. a(n) = A105343(n) if n>=1.
%e A330357 G.f. = 2 + 3*x + 4*x^2 + 7*x^3 + 10*x^4 + 15*x^5 + 20*x^6 + 27*x^7 + ...
%t A330357 Table[(2 n^2+9-(-1)^n)/4,{n,0,60}] (* or *) LinearRecurrence[{2,0,-2,1},{2,3,4,7},60] (* _Harvey P. Dale_, Apr 19 2023 *)
%o A330357 (PARI) {a(n) = (2*n^2 + 9 - (-1)^n)/4};
%Y A330357 Cf. A105343, A267459.
%K A330357 nonn,easy
%O A330357 0,1
%A A330357 _Michael Somos_, Dec 11 2019
%E A330357 Previous Mathematica program adjusted by _Harvey P. Dale_, Apr 19 2023