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 A013658 Discriminants of imaginary quadratic fields with class number 4 (negated). 26
 39, 55, 56, 68, 84, 120, 132, 136, 155, 168, 184, 195, 203, 219, 228, 259, 280, 291, 292, 312, 323, 328, 340, 355, 372, 388, 408, 435, 483, 520, 532, 555, 568, 595, 627, 667, 708, 715, 723, 760, 763, 772, 795, 955, 1003, 1012, 1027, 1227, 1243, 1387, 1411, 1435, 1507, 1555 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES H. Cohen, Course in Computational Alg. No. Theory, Springer, 1993, p. 229. LINKS Giovanni Resta, Table of n, a(n) for n = 1..54 (full sequence, from Weisstein's World of Mathematics) Rick L. Shepherd, Binary quadratic forms and genus theory, Master of Arts Thesis, University of North Carolina at Greensboro, 2013. Eric Weisstein's World of Mathematics, Class Number Sung Sik Woo, Cubic formula and cubic curves, Commun. Korean Math. Soc. 28 (2013), No. 2, pp. 209-224. MATHEMATICA Union[(-NumberFieldDiscriminant[Sqrt[-#]] &) /@ Select[Range[1250], NumberFieldClassNumber[Sqrt[-#]] == 4 &]] (* Jean-François Alcover, Jun 27 2012 *) PROG (PARI) ok(n)={isfundamental(-n) && quadclassunit(-n).no == 4} \\ Andrew Howroyd, Jul 20 2018 CROSSREFS Cf. A014603, A046005, A192322. Sequence in context: A070145 A133676 A317987 * A227735 A319983 A165346 Adjacent sequences:  A013655 A013656 A013657 * A013659 A013660 A013661 KEYWORD nonn,fini,full AUTHOR Eric Rains (rains(AT)caltech.edu) EXTENSIONS a(50)-a(54) added by Andrew Howroyd, Jul 20 2018 STATUS approved

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Last modified October 24 02:14 EDT 2018. Contains 316541 sequences. (Running on oeis4.)