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A191483 Even discriminants of imaginary quadratic fields, negated. 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Terms of A003657 that are not in A039957.

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-Fran├žois 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.

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

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Last modified January 29 10:34 EST 2020. Contains 331337 sequences. (Running on oeis4.)