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 A309136 #24 Dec 09 2024 11:51:35
%S A309136 0,1,4,9,15,16,25,27,33,36,37,45,49,51,53,55,57,60,64,75,81,85,95,99,
%T A309136 100,108,121,125,129,132,135,144,148,153,165,169,171,173,180,183,187,
%U A309136 193,196,204,209,212,213,215,220,225,228,229,240,241,243,249,255,256
%N A309136 Nonnegative integers of the form x^2+15*x*y-y^2.
%C A309136 Discriminant of indefinite binary quadratic form: 229.
%H A309136 Vincenzo Librandi, <a href="/A309136/b309136.txt">Table of n, a(n) for n = 1..1268</a>
%H A309136 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 A309136 Peter Luschny, <a href="https://oeis.org/wiki/User:Peter_Luschny/BinaryQuadraticForms#Implementation">Binary Quadratic Forms</a>
%H A309136 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)
%t A309136 Reap[For[n=0,n<=58,n++,If[Reduce[x^2+15*x*y-y^2==n,{x,y},Integers]=!=False,Sow[n]]]][[2,1]] (* _Vincenzo Librandi_, Nov 16 2024 *)
%t A309136 sol[t_]:=Solve[x^2+15*x*y-y^2==t,{x,y},Integers]; Select[Range[0,256],sol[#]!={}&] (* _Vincenzo Librandi_, Nov 25 2024 *)
%o A309136 (C++) See Jagy link.
%Y A309136 Primes in this sequence: A141166.
%K A309136 nonn
%O A309136 1,3
%A A309136 _Hugo Pfoertner_, Jul 14 2019