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 A228203 #31 Apr 22 2024 09:21:51
%S A228203 12,40,220,768,14808,51700,285520,996852,19220772,67106560,370604740,
%T A228203 1293913128,24948547248,87104263180,481044667000,1679498243292,
%U A228203 32383195107132,113061266501080,624395607161260,2179987425879888,42033362300510088,146753436814138660
%N A228203 x-values in the solution to x^2 - 13y^2 = 27.
%C A228203 This equation is used for worked examples in the Robertson paper.
%C A228203 (1/8)*a(n)^2 -5 is a term of A152741. [_Bruno Berselli_, Aug 17 2013]
%H A228203 Vincenzo Librandi, <a href="/A228203/b228203.txt">Table of n, a(n) for n = 1..1000</a>
%H A228203 John P. Robertson, <a href="https://web.archive.org/web/20180831180333/http://www.jpr2718.org/pell.pdf">Solving the generalized Pell equation x^2 - Dy^2 = N</a>
%H A228203 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,1298,0,0,0,-1).
%F A228203 G.f.: -4*x*(x-1)*(3*x^6+13*x^5+68*x^4+260*x^3+68*x^2+13*x+3) / ((x^4-36*x^2-1)*(x^4+36*x^2-1)).
%F A228203 a(n) = 1298*a(n-4)-a(n-8).
%t A228203 CoefficientList[Series[-4 (x - 1) (3 x^6 + 13 x^5 + 68 x^4 + 260 x^3 + 68 x^2 + 13 x+3) / ((x^4 - 36 x^2 - 1) (x^4 + 36 x^2 - 1)), {x, 0, 30}], x] (* _Vincenzo Librandi_, Aug 17 2013 *)
%t A228203 LinearRecurrence[{0,0,0,1298,0,0,0,-1},{12,40,220,768,14808,51700,285520,996852},30] (* _Harvey P. Dale_, Apr 22 2024 *)
%o A228203 (PARI) Vec(-4*x*(x-1)*(3*x^6+13*x^5+68*x^4+260*x^3+68*x^2+13*x+3)/((x^4-36*x^2-1)*(x^4+36*x^2-1)) + O(x^100))
%o A228203 (Magma) I:=[12,40,220,768,14808,51700,285520,996852]; [n le 8 select I[n] else 1298*Self(n-4)-Self(n-8): n in [1..30]]; // _Vincenzo Librandi_, Aug 17 2013
%Y A228203 Cf. A228204.
%K A228203 nonn,easy
%O A228203 1,1
%A A228203 _Colin Barker_, Aug 16 2013