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 A106256 #15 Jun 13 2015 00:51:48 %S A106256 1,3,17,43,237,599,3301,8343,45977,116203,640377,1618499,8919301, %T A106256 22542783,124229837,313980463,1730298417,4373183699,24099948001, %U A106256 60910591323,335668973597,848375094823,4675265682357,11816340736199 %N A106256 Numbers n such that 12*n^2 + 13 is a square. %H A106256 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (0,14,0,-1). %F A106256 Recurrence: a(1)=1, a(2)=3, a(3)=14*a(1)+a(2), a(4)=14*a(2)+a(1) then a(n)=14*a(n-2)-a(n-4). %F A106256 G.f.: x*(x+1)^3 / ((x^2-4*x+1)*(x^2+4*x+1)). - Corrected by _Colin Barker_, Apr 16 2014 %F A106256 a(2n) = 4*A007655(n)-A001570(n-1), a(2n+1) = 4*A007655(n)+A001570(n). %e A106256 12*1^2+13 = 5^2. %e A106256 12*3^2+13 = 11^2. %e A106256 12*17^2+13 = 59^2. %o A106256 (PARI) Vec(x*(x+1)^3/((x^2-4*x+1)*(x^2+4*x+1)) + O(x^100)) \\ _Colin Barker_, Apr 16 2014 %Y A106256 Cf. A106257. %K A106256 nonn,easy %O A106256 1,2 %A A106256 _Pierre CAMI_, Apr 28 2005 %E A106256 Edited by _Ralf Stephan_, Jun 01 2007