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 A006203 Discriminants of imaginary quadratic fields with class number 3 (negated). (Formerly M5131) 33
 23, 31, 59, 83, 107, 139, 211, 283, 307, 331, 379, 499, 547, 643, 883, 907 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also n such that Q(sqrt(-n)) has class number 3. Lubelski in 1936 proved that 907 is maximal term of this sequence. - Artur Jasinski, Oct 07 2011 REFERENCES H. Cohen, Course in Computational Alg. No. Theory, Springer, 1993, p. 514. Lubelski S. 1936 Zur Reduzibilitat von Polynomen in Kongruenzentheorie. Acta Arithmetica 1 pp. 169-183. J. M. Masley, Where are the number fields with small class number?, pp. 221-242 of Number Theory Carbondale 1979, Lect. Notes Math. 751 (1982). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Steven Arno, M. L. Robinson, Ferrell S. Wheeler, Imaginary quadratic fields with small odd class number, Acta Arith. 83 (1998), pp. 295-330. Kurt Heegner, Diophantische Analysis und Modulfunktionen, Matematische Zaitschrift, 1952, Vol. 56. p. 253. Keith Matthews, Tables of imaginary quadratic fields with small class numbers Eric Weisstein's World of Mathematics, Class Number. MATHEMATICA Union[ (-NumberFieldDiscriminant[ Sqrt[-#]] & ) /@ Select[ Range[1000], NumberFieldClassNumber[ Sqrt[-#]] == 3 & ]] (* Jean-François Alcover, Jan 04 2012 *) PROG (PARI) ok(n)={isfundamental(-n) && quadclassunit(-n).no == 3} \\ Andrew Howroyd, Jul 20 2018 (Sage) [n for n in (1..1000) if is_fundamental_discriminant(-n) and QuadraticField(-n, 'a').class_number()==3] # G. C. Greubel, Mar 01 2019 CROSSREFS Cf. A005847, A013658, A014602, A014603, A046002, ..., A046020. Cf. also A003173, A005847, ... Cf. A191410. Sequence in context: A064792 A030670 A030680 * A153635 A052160 A165985 Adjacent sequences:  A006200 A006201 A006202 * A006204 A006205 A006206 KEYWORD fini,nonn,full,nice AUTHOR STATUS approved

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Last modified October 14 07:06 EDT 2019. Contains 327995 sequences. (Running on oeis4.)