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%I #25 Jul 30 2018 22:59:44
%S 0,1,4,9,11,16,23,25,36,37,44,49,53,64,67,71,81,91,92,99,100,113,119,
%T 121,133,137,144,148,163,169,176,179,191,196,207,212,221,225,247,253,
%U 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 Numbers of the form x^2 + 9*x*y + y^2, 0 <= x <= y.
%C Discriminant 77.
%C 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 Gheorghe Coserea, <a href="/A316621/b316621.txt">Table of n, a(n) for n = 1..100001</a>
%o (PARI)
%o seq(M,k=9) = { \\ assume k >= 0
%o setintersect([1..M], setbinop((x,y)->x^2 + k*x*y + y^2, [0..1+sqrtint(M)]));
%o };
%o concat(0, seq(449))
%Y 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 nonn
%O 1,3
%A _Gheorghe Coserea_, Jul 29 2018
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