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%I #21 Mar 25 2022 09:13:24
%S 983,1231,1399,1607,1759,1879,1999,3271,3299,3943,4903,6007,6011,7699,
%T 8867,10531,10939,11003,11027,11383,11491,11779,11939,13411,14243,
%U 14723,15107,15739,16411,16547,17443,17627,17659,17747,18587,18787,18859,19051,19427
%N Discriminants of imaginary quadratic fields with class number 27 (negated).
%C Sequence contains 93 terms; largest is 103387.
%C The class group of Q[sqrt(-d)] is isomorphic to C_9 X C_3 for d = 3299, 19427, 34603, 89923, and 98443. For all other d in this sequence, the class group of Q[sqrt(-d)] is isomorphic to C_27.
%H Andy Huchala, <a href="/A351665/b351665.txt">Table of n, a(n) for n = 1..93</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ClassNumber.html">Class Number</a>
%o (Sage)
%o ls = [(QuadraticField(-n, 'a').discriminant(), QuadraticField(-n, 'a').class_number()) for n in (0..10000) if is_fundamental_discriminant(-n) and not is_square(n)];
%o [-a[0] for a in ls if a[1] == 27]
%o (PARI) isok(n) = {isfundamental(-n) && quadclassunit(-n).no == 27}; \\ _Michel Marcus_, Mar 02 2022
%Y Cf. A006203, A013658, A014602, A014603, A046002-A046020, A046125, A056987, A351664.
%K nonn,fini,full
%O 1,1
%A _Andy Huchala_, Feb 16 2022