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%I #15 Apr 03 2024 10:06:11
%S 0,3,7,12,13,15,17,27,28,35,47,48,52,53,60,63,65,67,68,75,85,93,97,
%T 108,112,117,123,135,137,140,147,153,157,167,175,177,183,188,192,193,
%U 208,212,217,227,233,235,240,243,252,257,260,263,265,268
%N Nonnegative numbers represented by the indefinite quadratic form 3x^2+13xy-3y^2.
%C Discriminant 205.
%C 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 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 Will Jagy, <a href="/A243655/a243655_2.txt">Sample output from Conway_Positive_All.cc</a>
%H 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 (C++) // Jagy's program, see link.
%o // Conway_Positive_All 3 13 -3 500
%Y Primes: A243706.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Jun 17 2014