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 A351666 #21 Feb 16 2025 08:34:03
%S A351666 831,935,1095,1311,1335,1364,1455,1479,1496,1623,1703,1711,1855,1976,
%T A351666 2024,2055,2120,2127,2324,2359,2431,2455,2564,2607,2616,2703,3224,
%U A351666 3272,3396,3419,3487,3535,3572,3576,3608,3624,3731,3848,3995,4040,4183,4279,4344
%N A351666 Discriminants of imaginary quadratic fields with class number 28 (negated).
%C A351666 Sequence contains 457 terms; largest is 126043.
%C A351666 The class groups associated to 174 of the above discriminants are isomorphic to C_28, and the remaining 283 have a class group isomorphic to C_14 X C_2.
%H A351666 Andy Huchala, <a href="/A351666/b351666.txt">Table of n, a(n) for n = 1..457</a>
%H A351666 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ClassNumber.html">Class Number</a>
%o A351666 (Sage)
%o A351666 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 A351666 [-a[0] for a in ls if a[1] == 28]
%o A351666 (PARI) isok(n) = {isfundamental(-n) && quadclassunit(-n).no == 28}; \\ _Michel Marcus_, Mar 02 2022
%Y A351666 Cf. A006203, A013658, A014602, A014603, A046002-A046020, A046125, A056987, A351664.
%K A351666 nonn,fini,full
%O A351666 1,1
%A A351666 _Andy Huchala_, Feb 16 2022