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%I #22 Oct 15 2018 15:33:29
%S 39,55,56,68,136,155,184,203,219,259,260,264,276,291,292,308,323,328,
%T 355,388,456,552,564,568,580,616,651,667,723,763,772,820,852,868,915,
%U 952,955,987,1003,1027,1032,1060,1128,1131,1140,1204,1227,1240,1243,1288,1387,1411,1443
%N Discriminants of imaginary quadratic fields with 2 classes per genus, negated.
%C Fundamental terms of A317987.
%C k is a term iff the class group of Q[sqrt(-k)], or the form class group of positive binary quadratic forms with discriminant -k is isomorphic to (C_2)^r X C_4.
%C This is a subsequence of A133676, so it's finite. It seems that this sequence has 161 terms, the largest being 40755.
%H Jianing Song, <a href="/A319983/b319983.txt">Table of n, a(n) for n = 1..161</a>
%H Rick L. Shepherd, <a href="http://libres.uncg.edu/ir/uncg/f/Shepherd_uncg_0154M_11099.pdf">Binary quadratic forms and genus theory</a>, Master of Arts Thesis, University of North Carolina at Greensboro, 2013.
%e See examples in A317987.
%o (PARI) isA319983(n) = isfundamental(-n) && 2^(1+#quadclassunit(-n)[2])==quadclassunit(-n)[1]
%Y Cf. A003644, A133676.
%Y Subsequence of A317987.
%K nonn,fini
%O 1,1
%A _Jianing Song_, Oct 02 2018
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