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 A328825 #42 May 17 2021 08:41:43 %S A328825 23,31,44,59,76,83,92,107,108,124,139,172,211,243,268,283,307,331,379, %T A328825 499,547,643,652,883,907 %N A328825 Negative discriminants with form class group isomorphic to C_3 (negated). %C A328825 Also negative discriminants with form class number 3. %C A328825 Conjecture: this sequence is finite and this is the full list. %C A328825 The fundamental terms are listed in A006203, and that is a full sequence. %C A328825 From _Jianing Song_, May 17 2021: (Start) %C A328825 Equivalently, negative discriminants of orders whose class group is isomorphic to C_3 (negated). %C A328825 The known even terms are all congruent to 12 modulo 16. Among the known even terms, k/4 is either here or in A133675. What's the reason for that? %C A328825 Among the known terms, k is in A023679 if and only if k is in this sequence and k/4 is not. Is there a connection between these two sequences? (End) %H A328825 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. %o A328825 (PARI) isA328825(d) = (d>0) && ((d%4==0)||(d%4==3)) && quadclassunit(-d)[2]==[3] \\ Corrected by _Jianing Song_, May 17 2021 %Y A328825 Cf. A133675 (negative discriminants with form class group isomorphic to the trivial group), A322710 (isomorphic to C_2), this sequence (isomorphic to C_3), A329182 (isomorphic to C_2 X C_2), A330219 (isomorphic to C_4). %Y A328825 Cf. A006203, A023679. %K A328825 nonn,more %O A328825 1,1 %A A328825 _Jianing Song_, Dec 05 2019