A191483 Even discriminants of imaginary quadratic fields, negated.

4, 8, 20, 24, 40, 52, 56, 68, 84, 88, 104, 116, 120, 132, 136, 148, 152, 164, 168, 184, 212, 228, 232, 244, 248, 260, 264, 276, 280, 292, 296, 308, 312, 328, 340, 344, 356, 372, 376, 388, 404, 408, 420, 424, 436, 440, 452, 456, 472, 488, 516, 520, 532, 536, 548

Offset

1,1

Comments

Terms of A003657 that are not in A039957.

The asymptotic density of this sequence is 1/Pi^2 (A092742). - Amiram Eldar, Feb 23 2021

Links

Andrew Howroyd, Table of n, a(n) for n = 1..1000

Formula

Complement(A003657, A039957).

a(n) = 4*A089269(n). - Andrew Howroyd, Jul 25 2018

Mathematica

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@# &]
(* Second program: *)
Select[Range[600], Mod[#, 4] == 0 && SquareFreeQ[#/4] && Mod[#, 16] != 12&] (* Jean-François Alcover, Jul 25 2019, after Andrew Howroyd *)

Prog

(PARI) ok(n)={isfundamental(-n) && n%2==0} \\ Andrew Howroyd, Jul 25 2018
(PARI) ok(n)={n%4==0 && issquarefree(n/4) && n%16<>12} \\ Andrew Howroyd, Jul 25 2018

Crossrefs

Cf. A003657, A039957, A089269, A092742.

Sequence in context: A061814 A087254 A160726 * A062717 A084922 A180794

Adjacent sequences: A191480 A191481 A191482 * A191484 A191485 A191486

Keyword

easy,nonn

Author

Robert G. Wilson v, Jun 04 2011

Status

approved