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 A035120 #17 Feb 16 2025 08:32:37 %S A035120 40,60,65,85,104,105,120,136,140,145,156,165,168,185,204,205,220,221, %T A035120 229,232,257,264,265,273,280,285,296,305,312,316,321,328,345,348,357, %U A035120 364,365,377,380,385,401,408,424,429,440,444,445,456,460,465,469,473 %N A035120 Discriminants of real quadratic number fields with class number >= 2. %D A035120 H. Cohen, Advanced Topics in Computational Number Theory, Springer, 2000, p. 534. %D A035120 H. Hasse, Number Theory, Springer-Verlag, NY, 1980, p. 576. %H A035120 T. D. Noe, <a href="/A035120/b035120.txt">Table of n, a(n) for n = 1..1000</a> %H A035120 X.-F. Roblot and Igor Schein, <a href="http://euler.univ-lyon1.fr/home/roblot/tables.html#1">Hilbert class field of totally real fields of degree 2, 3 and 4</a>. %H A035120 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ClassNumber.html">Class Number</a> %t A035120 Select[Range[500], NumberFieldDiscriminant[Sqrt[#]] == # && NumberFieldClassNumber[Sqrt[#]] >= 2 & ] (* _Jean-François Alcover_, Jul 04 2013 *) %Y A035120 Cf. A003656, A094619. %K A035120 nonn,nice,easy %O A035120 1,1 %A A035120 _N. J. A. Sloane_ %E A035120 More terms from Antonio G. Astudillo (afg_astudillo(AT)hotmail.com), May 15 2002