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 A243705 #15 Apr 03 2024 10:06:11 %S A243705 0,3,7,12,13,15,17,27,28,35,47,48,52,53,60,63,65,67,68,75,85,93,97, %T A243705 108,112,117,123,135,137,140,147,153,157,167,175,177,183,188,192,193, %U A243705 208,212,217,227,233,235,240,243,252,257,260,263,265,268 %N A243705 Nonnegative numbers represented by the indefinite quadratic form 3x^2+13xy-3y^2. %C A243705 Discriminant 205. %C A243705 12*a(n) has the form z^2 - 205*y^2, where z = 6*x+13*y. In fact, this is a particular case of the following identity on the numbers of the form a*x^2+b*x*y+c*y^2: 4*a*(a*x^2+b*x*y+c*y^2) = (2*a*x+b*y)^2-(b^2 -4*a*c)*y^2. [_Bruno Berselli_, Jun 20 2014] %H A243705 Will Jagy, <a href="/A243655/a243655.txt">C++ program Conway_Positive_All.cc to find all positive numbers represented by an indefinite binary quadratic form</a> %H A243705 Will Jagy, <a href="/A243655/a243655_2.txt">Sample output from Conway_Positive_All.cc</a> %H A243705 N. J. A. Sloane et al., <a href="https://oeis.org/wiki/Binary_Quadratic_Forms_and_OEIS">Binary Quadratic Forms and OEIS</a> (Index to related sequences, programs, references) %o A243705 (C++) // Jagy's program, see link. %o A243705 // Conway_Positive_All 3 13 -3 500 %Y A243705 Primes: A243706. %K A243705 nonn %O A243705 1,2 %A A243705 _N. J. A. Sloane_, Jun 17 2014