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 A305416 #35 Sep 25 2019 07:47:02
%S A305416 420,660,840,1092,1155,1320,1380,1428,1540,1848,1995,3003,3315
%N A305416 Negated discriminants of imaginary quadratic number fields whose class group is isomorphic to the Klein 8-group, C_2 x C_2 x C_2.
%C A305416 Intersection of A046005 and A003644. Note that A003644 = A014602 union A014603 union A192322 union {a(n)} union {5460}. - _Jianing Song_, Jul 12 2018
%H A305416 Alexandre Gélin, Everett W. Howe, and Christophe Ritzenthaler, <a href="https://arxiv.org/abs/1806.03826">Principally Polarized Squares of Elliptic Curves with Field of Moduli Equal To Q</a>, arXiv:1806.03826 [math.NT], 2018 (see table 1 page 4).
%t A305416 A046005 = Import["https://oeis.org/A046005/b046005.txt", "Table"][[All, 2]];
%t A305416 A003644 = Import["https://oeis.org/A003644/b003644.txt", "Table"][[All, 2]];
%t A305416 A046005 ~Intersection~ A003644 (* _Jean-François Alcover_, Sep 25 2019 *)
%o A305416 (PARI) ok(n)={isfundamental(-n) && [2, 2, 2] == quadclassunit(-n).cyc} \\ _Andrew Howroyd_, Jul 20 2018
%Y A305416 Cf. A003644, A014602, A014603, A192322.
%Y A305416 Subsequence of A046005 and A003644.
%K A305416 nonn,fini,full
%O A305416 1,1
%A A305416 _Vincenzo Librandi_, Jun 12 2018