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 A237250 #15 Jun 13 2015 00:54:58 %S A237250 2,3,5,10,18,37,67,138,250,515,933,1922,3482,7173,12995,26770,48498, %T A237250 99907,180997,372858,675490,1391525,2520963,5193242,9408362,19381443, %U A237250 35112485,72332530,131041578,269948677,489053827,1007462178,1825173730,3759900035 %N A237250 Values of x in the solutions to x^2 - 4xy + y^2 + 11 = 0, where 0 < x < y. %C A237250 The corresponding values of y are given by a(n+2). %C A237250 Positive values of x (or y) satisfying x^2 - 14xy + y^2 + 176 = 0. %H A237250 Colin Barker, <a href="/A237250/b237250.txt">Table of n, a(n) for n = 1..1000</a> %H A237250 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,4,0,-1). %F A237250 a(n) = 4*a(n-2)-a(n-4). %F A237250 G.f.: -x*(x-1)*(x+2)*(2*x+1) / (x^4-4*x^2+1). %e A237250 10 is in the sequence because (x, y) = (10, 37) is a solution to x^2 - 4xy + y^2 + 11 = 0. %o A237250 (PARI) Vec(-x*(x-1)*(x+2)*(2*x+1)/(x^4-4*x^2+1) + O(x^100)) %Y A237250 Cf. A001075, A001835, A003500, A082841. %K A237250 nonn,easy %O A237250 1,1 %A A237250 _Colin Barker_, Feb 05 2014