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 A003648 M0210 #9 Jan 27 2014 08:57:35 %S A003648 1,2,2,2,2,2,2,4,2,2,2,2,4,2,4,4,2,4,4,2,2,2,4,4,2,2,2,4,2,4,2,2,4,6, %T A003648 4,2,2,4,4,2,4,4,2,2,2,4,4,4,4,2,4,2,4,2,4,2,2,4,2,6,4,4,2,4,4,2,4,2, %U A003648 2,2,4,4,4,2,4,4,4,4,4,2,4,8,2,2,4,2,8,2,2,4,2,8,4,6,8,2,4,8,12,4,2,4,4,2 %N A003648 Class number of quadratic forms with discriminant 4n, n == 2,3^( mod 4). %D A003648 D. A. Buell, Binary Quadratic Forms. Springer-Verlag, NY, 1989, pp. 224-241. %D A003648 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %Y A003648 Cf. A003647. %K A003648 nonn %O A003648 2,2 %A A003648 _N. J. A. Sloane_, _Mira Bernstein_