This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A351677 #12 Feb 16 2025 08:34:03 %S A351677 1439,2207,2791,3767,3919,4111,5099,5119,6199,6779,9059,9967,10091, %T A351677 10163,10399,10567,10667,11743,12539,13163,13523,14843,14867,15607, %U A351677 16087,16139,16787,17383,18127,21851,23027,24499,26539,27827,30211,30347,30803,32027,32491 %N A351677 Discriminants of imaginary quadratic fields with class number 39 (negated). %C A351677 Sequence contains 115 terms; largest is 253507. %C A351677 The class group of Q[sqrt(-d)] is isomorphic to C_39 for all d in this sequence. %H A351677 Andy Huchala, <a href="/A351677/b351677.txt">Table of n, a(n) for n = 1..115</a> %H A351677 Mark Watkins, <a href="https://doi.org/10.1090/S0025-5718-03-01517-5">Class numbers of imaginary quadratic fields</a>, Mathematics of Computation, 73, pp. 907-938. %H A351677 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ClassNumber.html">Class Number</a> %o A351677 (Sage) %o A351677 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 A351677 [-a[0] for a in ls if a[1] == 39] %Y A351677 Cf. A006203, A013658, A014602, A014603, A046002-A046020, A046125, A056987, A351664-A351680. %K A351677 nonn,fini,full %O A351677 1,1 %A A351677 _Andy Huchala_, Mar 27 2022