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A133288 Negative discriminants with form class group of exponent 2 (negated). 5
15, 20, 24, 32, 35, 36, 40, 48, 51, 52, 60, 64, 72, 75, 84, 88, 91, 96, 99, 100, 112, 115, 120, 123, 132, 147, 148, 160, 168, 180, 187, 192, 195, 228, 232, 235, 240, 267, 280, 288, 312, 315, 340, 352, 372, 403, 408, 420, 427, 435, 448, 480, 483, 520, 532, 555, 595, 627, 660, 672, 708, 715, 760 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

D. A. Cox, Primes of the form x^2+ny^2, Wiley, New York, 1989.

D. E. Flath, Introduction to Number Theory, Wiley-Interscience, 1989.

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..88

PROG

(PARI) ok(n)={(-n)%4<2 && quadclassunit(-n).no > 1 && !#select(k->k<>2, quadclassunit(-n).cyc)} \\ Andrew Howroyd, Jul 20 2018

CROSSREFS

Cf. A003171 is the disjoint union of A133675 and this sequence.

Sequence in context: A113529 A214410 A102495 * A322710 A316743 A014603

Adjacent sequences:  A133285 A133286 A133287 * A133289 A133290 A133291

KEYWORD

fini,nonn

AUTHOR

David Brink, Dec 30 2007

STATUS

approved

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Last modified March 28 14:24 EDT 2020. Contains 333089 sequences. (Running on oeis4.)