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 A039958 #12 Mar 05 2020 02:28:50 %S A039958 1,-1,1,2,-1,1,1,2,3,-2,1,2,-1,1,2,4,-1,3,1,2,1,1,1,2,5,-2,3,2,-1,2,1, %T A039958 4,1,2,2,6,-1,1,2,2,-1,2,1,2,3,1,1,4,7,5,2,2,-1,3,2,2,1,-2,1,2,-1,1,3, %U A039958 8,-2,2,1,2,1,2,1,6,-1,-2,5,2,1,2,3,4,9,-4,1,2,-2,1,2,2,-1,3,2,2,1,1,2,4,-1,7,3,10 %N A039958 Class number of maximal order in real quadratic field of radicand n. %C A039958 Mollin gives a table for n < 10000. %D A039958 R. A. Mollin, Quadratics, CRC Press, 1996, Table C1. %K A039958 sign,easy,nice %O A039958 1,4 %A A039958 _R. K. Guy_, _N. J. A. Sloane_