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 A135658 #5 Jan 18 2021 09:21:35
%S A135658 4,15,16,24,28,36,40,55,60,63,64,87,88,96,100,112,124,132,135,144,159,
%T A135658 160,168,175,196,216,220,231,232,240,247
%N A135658 Nonprimes of the form 4x^2-4xy+7y^2.
%C A135658 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 A135658 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 A135658 Cf. A107006, A124477, A135657.
%K A135658 nonn
%O A135658 1,1
%A A135658 _Artur Jasinski_, Nov 25 2007