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%I #21 Feb 23 2021 05:22:32
%S 4,8,20,24,40,52,56,68,84,88,104,116,120,132,136,148,152,164,168,184,
%T 212,228,232,244,248,260,264,276,280,292,296,308,312,328,340,344,356,
%U 372,376,388,404,408,420,424,436,440,452,456,472,488,516,520,532,536,548
%N Even discriminants of imaginary quadratic fields, negated.
%C Terms of A003657 that are not in A039957.
%C The asymptotic density of this sequence is 1/Pi^2 (A092742). - _Amiram Eldar_, Feb 23 2021
%H Andrew Howroyd, <a href="/A191483/b191483.txt">Table of n, a(n) for n = 1..1000</a>
%F Complement(A003657, A039957).
%F a(n) = 4*A089269(n). - _Andrew Howroyd_, Jul 25 2018
%t FundamentalDiscriminantQ[n_Integer] := n != 1 && (Mod[n, 4] == 1 || ! Unequal[ Mod[n, 16], 8, 12]) && SquareFreeQ[n/2^IntegerExponent[n, 2]] (* via Eric E. Weisstein *); -Select[-Range@550, FundamentalDiscriminantQ@# && EvenQ@# &]
%t (* Second program: *)
%t Select[Range[600], Mod[#, 4] == 0 && SquareFreeQ[#/4] && Mod[#, 16] != 12&] (* _Jean-François Alcover_, Jul 25 2019, after _Andrew Howroyd_ *)
%o (PARI) ok(n)={isfundamental(-n) && n%2==0} \\ _Andrew Howroyd_, Jul 25 2018
%o (PARI) ok(n)={n%4==0 && issquarefree(n/4) && n%16<>12} \\ _Andrew Howroyd_, Jul 25 2018
%Y Cf. A003657, A039957, A089269, A092742.
%K easy,nonn
%O 1,1
%A _Robert G. Wilson v_, Jun 04 2011
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