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 A237133 #23 Jun 13 2015 00:54:58
%S A237133 4,5,7,11,17,28,44,73,115,191,301,500,788,1309,2063,3427,5401,8972,
%T A237133 14140,23489,37019,61495,96917,160996,253732,421493,664279,1103483,
%U A237133 1739105,2888956,4553036,7563385,11920003,19801199,31206973,51840212,81700916,135719437
%N A237133 Values of x in the solutions to x^2 - 3xy + y^2 + 19 = 0, where 0 < x < y.
%C A237133 The corresponding values of y are given by a(n+2).
%C A237133 Positive values of x (or y) satisfying x^2 - 18xy + y^2 + 1216 = 0.
%H A237133 Colin Barker, <a href="/A237133/b237133.txt">Table of n, a(n) for n = 1..1000</a>
%H A237133 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,3,0,-1).
%F A237133 a(n) = 3*a(n-2)-a(n-4).
%F A237133 G.f.: -x*(x-1)*(4*x^2+9*x+4) / ((x^2-x-1)*(x^2+x-1)).
%F A237133 a(n) = (1/2) * (F(n+4) + (-1)^n*F(n-5)), n>4, with F the Fibonacci numbers (A000045). - _Ralf Stephan_, Feb 05 2014
%e A237133 11 is in the sequence because (x, y) = (11, 28) is a solution to x^2 - 3xy + y^2 + 19 = 0.
%t A237133 LinearRecurrence[{0,3,0,-1},{4,5,7,11},40] (* _Harvey P. Dale_, Dec 15 2014 *)
%o A237133 (PARI) Vec(-x*(x-1)*(4*x^2+9*x+4)/((x^2-x-1)*(x^2+x-1)) + O(x^100))
%Y A237133 Cf. A001519, A005248, A055819, A237132, A218735.
%K A237133 nonn,easy
%O A237133 1,1
%A A237133 _Colin Barker_, Feb 04 2014