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 A243702 #26 May 04 2024 11:01:39
%S A243702 0,1,4,5,9,16,20,21,25,36,39,45,49,51,59,64,80,81,84,91,100,105,119,
%T A243702 121,125,131,139,141,144,156,159,169,180,189,195,196,201,204,221,225,
%U A243702 236,241,245,255,256,269,271,279,289,291,295,320,324,329,336,351,359
%N A243702 Nonnegative numbers represented by the indefinite quadratic form x^2 + 13xy - 9y^2.
%C A243702 Discriminant 205.
%H A243702 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 A243702 Will Jagy, <a href="/A243655/a243655_2.txt">Sample output from Conway_Positive_All.cc</a>
%H A243702 Peter Luschny, <a href="https://github.com/PeterLuschny/BinaryQuadraticForms">Binary Quadratic Forms</a>, GitHub 2024.
%H A243702 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 A243702 (C++) // Jagy's program, see link.
%o A243702 // Conway_Positive_All 1 13 -9 500
%o A243702 (SageMath)
%o A243702 load('https://raw.githubusercontent.com/PeterLuschny/BinaryQuadraticForms/main/BinaryQF.sage')
%o A243702 Q = binaryQF([1, 13, -9])
%o A243702 print(Q.represented_positives(360, 'all')) # '0' is missing as indicated by the function name. # _Peter Luschny_, May 04 2024
%Y A243702 Cf. A243701 (primes), A243702 (this sequence), A372518 (primitively).
%K A243702 nonn
%O A243702 1,3
%A A243702 _N. J. A. Sloane_, Jun 17 2014