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 A200407 #21 May 06 2024 06:54:53
%S A200407 1,9,131,209,3051,44539,71059,1037331,15143129,24159851,352689489,
%T A200407 5148619321,8214278281,119913388929,1750515426011,2792830455689,
%U A200407 40770199546371,595170096224419,949554140655979,13861747932377211,202356082200876449,322845614992577171
%N A200407 The x-values in the solution to 19*x^2 - 18 = y^2.
%C A200407 When are both n+1 and 19*n+1 perfect squares? This gives the equation 19*x^2-18=y^2.
%H A200407 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,340,0,0,-1).
%F A200407 a(n) = 340*a(n-3)+a(n-6), a(1)=1, a(2)=9, a(3)=131, a(4)=209, a(5)=3051, a(6)=44539.
%F A200407 G.f.: -x*(x-1)*(x^4+10*x^3+141*x^2+10*x+1) / (x^6-340*x^3+1). - _Colin Barker_, Sep 01 2013
%e A200407 a(7)=340*209-1=71059.
%t A200407 LinearRecurrence[{0, 0, 340, 0, 0, -1}, {1, 9, 131, 209, 3051, 44539}, 50]
%o A200407 (PARI) Vec(-x*(x-1)*(x^4+10*x^3+141*x^2+10*x+1)/(x^6-340*x^3+1) + O(x^100)) \\ _Colin Barker_, Sep 01 2013
%Y A200407 Cf. A199773, A199774, A199798, A200409.
%K A200407 nonn,easy
%O A200407 1,2
%A A200407 _Sture Sjöstedt_, Nov 17 2011