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 A237351 #25 Apr 23 2023 13:24:20
%S A237351 3,5,12,17,20,21,27,35,41,45,47,48,59,68,75,80,83,84,89,101,108,111,
%T A237351 119,125,129,131,140,147,153,164,167,173,180,185,188,189,192,201,215,
%U A237351 227,236,237,243,245,251,255,257,269,272,287,293,300,311,315,320,327
%N A237351 Positive integers k such that x^2 - 5xy + y^2 + k = 0 has integer solutions.
%C A237351 See comments on method used in A084917.
%C A237351 The equivalent sequence for x^2 - 3xy + y^2 + k = 0 is A031363.
%C A237351 The equivalent sequence for x^2 - 4xy + y^2 + k = 0 is A084917.
%C A237351 Positive numbers of the form 3x^2 - 7y^2. - _Jon E. Schoenfield_, Jun 03 2022
%H A237351 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)
%e A237351 12 is in the sequence because x^2 - 5xy + y^2 + 12 = 0 has integer solutions, for example, (x, y) = (2, 8).
%t A237351 Select[Range[350],Length[FindInstance[x^2-5x y+y^2+#==0,{x,y},Integers]]>0&] (* _Harvey P. Dale_, Apr 23 2023 *)
%Y A237351 Cf. A004253 (k = 3), A237254 (k = 5), A237255 (k = 17).
%Y A237351 Cf. A031363, A084917.
%Y A237351 For primes see A141160.
%K A237351 nonn
%O A237351 1,1
%A A237351 _Colin Barker_, Feb 06 2014