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 A351680 #11 Feb 16 2025 08:34:03 %S A351680 1959,2183,2911,3039,3176,3687,3831,4039,4103,4184,4735,4904,4952, %T A351680 5288,5935,5959,6179,6452,6487,6611,6623,6632,6836,7447,7604,7811, %U A351680 7892,7988,8459,8552,8579,8744,8852,9368,9428,9607,10231,10643,10772,10996,11023,11099 %N A351680 Discriminants of imaginary quadratic fields with class number 42 (negated). %C A351680 Sequence contains 339 terms; largest is 280267. %C A351680 The class group of Q[sqrt(-d)] is isomorphic to C_42 for all d in this sequence. %H A351680 Andy Huchala, <a href="/A351680/b351680.txt">Table of n, a(n) for n = 1..339</a> %H A351680 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 A351680 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ClassNumber.html">Class Number</a> %o A351680 (Sage) %o A351680 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 A351680 [-a[0] for a in ls if a[1] == 42] %Y A351680 Cf. A006203, A013658, A014602, A014603, A046002-A046020, A046125, A056987, A351664-A351679. %K A351680 nonn,fini,full %O A351680 1,1 %A A351680 _Andy Huchala_, Mar 28 2022