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 A316621 #25 Jul 30 2018 22:59:44
%S A316621 0,1,4,9,11,16,23,25,36,37,44,49,53,64,67,71,81,91,92,99,100,113,119,
%T A316621 121,133,137,144,148,163,169,176,179,191,196,207,212,221,225,247,253,
%U A316621 256,268,275,284,287,289,317,323,324,331,333,361,364,368,379,389,396,400,401,407,421,427,441,443,449
%N A316621 Numbers of the form x^2 + 9*x*y + y^2, 0 <= x <= y.
%C A316621 Discriminant 77.
%C A316621 In general, for k>=0 the positive part of the set S = {x^2 - k*x*y + y^2: x,y in Z} is given by the numbers of the form x^2 + k*x*y + y^2 with 0 <= x <= y natural numbers.
%H A316621 Gheorghe Coserea, <a href="/A316621/b316621.txt">Table of n, a(n) for n = 1..100001</a>
%o A316621 (PARI)
%o A316621 seq(M,k=9) = { \\ assume k >= 0
%o A316621 setintersect([1..M], setbinop((x,y)->x^2 + k*x*y + y^2, [0..1+sqrtint(M)]));
%o A316621 };
%o A316621 concat(0, seq(449))
%Y A316621 Numbers representable as x^2 + k*x*y + y^2 with 0 <= x <= y, for k=0..9: A001481(k=0), A003136(k=1), A000290(k=2), A031363(k=3), A084916(k=4), A243172(k=5), A242663(k=6), A243174(k=7), A243188(k=8), this sequence.
%K A316621 nonn
%O A316621 1,3
%A A316621 _Gheorghe Coserea_, Jul 29 2018