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 A228204 #24 Feb 11 2024 04:19:34
%S A228204 3,11,61,213,4107,14339,79189,276477,5330883,18612011,102787261,
%T A228204 358866933,6919482027,24158375939,133417785589,465809002557,
%U A228204 8981482340163,31357553356811,173176182907261,604619726452053,11657957158049547,40702080098764739
%N A228204 y-values in the solution to x^2 - 13y^2 = 27.
%C A228204 This equation is used for worked examples in the Robertson paper.
%H A228204 Vincenzo Librandi, <a href="/A228204/b228204.txt">Table of n, a(n) for n = 1..1000</a>
%H A228204 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 A228204 <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 A228204 G.f.: x*(x+1)*(3*x^6+8*x^5+53*x^4+160*x^3+53*x^2+8*x+3) / ((x^4-36*x^2-1)*(x^4+36*x^2-1)).
%F A228204 a(n) = 1298*a(n-4)-a(n-8).
%t A228204 CoefficientList[Series[(x + 1) (3 x^6 + 8 x^5 + 53 x^4 + 160 x^3 + 53 x^2 + 8 x + 3) / ((x^4 - 36 x^2 - 1) (x^4 + 36 x^2 - 1)), {x, 0, 30}], x] (* _Vincenzo Librandi_, Aug 17 2013 *)
%t A228204 LinearRecurrence[{0,0,0,1298,0,0,0,-1},{3,11,61,213,4107,14339,79189,276477},30] (* _Harvey P. Dale_, Aug 26 2013 *)
%o A228204 (PARI) Vec(x*(x+1)*(3*x^6+8*x^5+53*x^4+160*x^3+53*x^2+8*x+3)/((x^4-36*x^2-1)*(x^4+36*x^2-1)) + O(x^100))
%o A228204 (Magma) I:=[3,11,61,213,4107,14339,79189,276477]; [n le 8 select I[n] else 1298*Self(n-4)-Self(n-8): n in [1..30]]; // _Vincenzo Librandi_, Aug 17 2013
%Y A228204 Cf. A228203.
%K A228204 nonn,easy
%O A228204 1,1
%A A228204 _Colin Barker_, Aug 16 2013