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Nonprimes of the form 4x^2-4xy+7y^2.
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%I #5 Jan 18 2021 09:21:35

%S 4,15,16,24,28,36,40,55,60,63,64,87,88,96,100,112,124,132,135,144,159,

%T 160,168,175,196,216,220,231,232,240,247

%N Nonprimes of the form 4x^2-4xy+7y^2.

%C Because 4x^2-4*x*y+7*y^2 = (2*x-y)^2+6*y^2, this is a subsequence of A002481. - _R. J. Mathar_, Jan 18 2021

%t Do[Do[w = 4x^2 - 4x y + 7y^2; If[w > 0, If[PrimeQ[w],[null], AppendTo[a, w]]], {x, 0, 100}], {y, 0, 100}]; Union[a]

%Y Cf. A107006, A124477, A135657.

%K nonn

%O 1,1

%A _Artur Jasinski_, Nov 25 2007