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 A003649 M0054 #29 Jun 02 2017 12:31:57
%S A003649 1,1,1,1,1,2,1,1,1,2,1,1,1,1,1,2,1,2,1,1,2,2,1,1,2,1,2,1,1,1,2,1,2,1,
%T A003649 2,1,1,1,2,2,1,1,2,1,1,2,1,2,3,4,1,2,1,2,1,2,1,1,2,1,1,2,1,2,2,1,1,2,
%U A003649 2,1,2,2,1,2,2,2,1,1,4,1,1,1,1,2,1,1,3,2,4,2,1,1,2,2,1,1,2,1,1,2,1,1,4,1,2
%N A003649 Class number of real quadratic field Q(sqrt f), where f is the n-th squarefree number A005117(n).
%D A003649 Şaban Alaca & Kenneth S. Williams, Introductory Algebraic Number Theory. Cambridge: Cambridge University Press (2004): 322-326, Theorem 12.6.1, Example 12.6.7, Table 8.
%D A003649 D. A. Buell, Binary Quadratic Forms. Springer-Verlag, NY, 1989, pp. 224-241.
%D A003649 M. Pohst and H. Zassenhaus, Algorithmic Algebraic Number Theory, Cambridge Univ. Press, 1989, p. 432.
%D A003649 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A003649 T. D. Noe, <a href="/A003649/b003649.txt">Table of n, a(n) for n = 2..6083</a> (squarefree numbers < 10000)
%H A003649 S. R. Finch, <a href="/A000924/a000924.pdf">Class number theory</a> [Cached copy, with permission of the author]
%H A003649 <a href="/index/Qua#quadfield">Index entries for sequences related to quadratic fields</a>
%t A003649 DeleteCases[Table[Boole[FreeQ[FactorInteger[n], {_, k_ /; k > 2}]] * NumberFieldClassNumber[Sqrt[n]], {n, 100}], 0] (* _Alonso del Arte_, Aug 26 2014 *)
%o A003649 (PARI) for(n=2,1e3,if(issquarefree(n),print1(qfbclassno(n*if(n%4>1, 4, 1))", "))) \\ _Charles R Greathouse IV_, Feb 19 2013
%Y A003649 Cf. A000924.
%K A003649 nonn
%O A003649 2,6
%A A003649 _N. J. A. Sloane_ and _Mira Bernstein_