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%I M0112 #36 Apr 14 2019 10:43:24
%S 1,1,1,1,1,2,1,2,3,2,3,2,4,2,1,5,2,2,4,4,3,1,4,7,5,3,4,6,2,2,8,5,6,3,
%T 8,2,6,10,4,2,5,5,4,4,3,10,2,7,6,4,10,1,8,11,4,5,8,4,2,13,4,9,4,3,6,
%U 14,4,7,5,4,12,2
%N Class number of forms with discriminant -A003657(n), or equivalently class number of imaginary quadratic field with discriminant -A003657(n).
%D D. A. Buell, Binary Quadratic Forms. Springer-Verlag, NY, 1989, pp. 224-241.
%D H. Cohen, Course in Computational Alg. No. Theory, Springer, 1993, p. 514.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H T. D. Noe, <a href="/A006641/b006641.txt">Table of n, a(n) for n=1..3000</a>
%H S. R. Finch, <a href="http://www.people.fas.harvard.edu/~sfinch/">Class number theory</a>
%H Steven R. Finch, <a href="/A000924/a000924.pdf">Class number theory</a> [Cached copy, with permission of the author]
%H Rick L. Shepherd, <a href="http://libres.uncg.edu/ir/uncg/f/Shepherd_uncg_0154M_11099.pdf">Binary quadratic forms and genus theory</a>, Master of Arts Thesis, University of North Carolina at Greensboro, 2013.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ClassNumber.html">Class Number</a>
%t FundamentalDiscriminantQ[n_Integer] := n != 1 && (Mod[n, 4] == 1 || !Unequal[ Mod[n, 16], 8, 12]) && SquareFreeQ[n/2^IntegerExponent[n, 2]] (* via _Eric W. Weisstein_ *);
%t NumberFieldClassNumber@ Sqrt@ # & /@ Select[-Range@ 300, FundamentalDiscriminantQ]
%o (PARI) for(n=1, 300, if(isfundamental(-n), print1(quadclassunit(-n).no, ", "))) \\ _Andrew Howroyd_, Jul 23 2018
%o (Sage) [1] + [QuadraticField(-n, 'a').class_number() for n in (0..200) if is_fundamental_discriminant(-n) and not is_square(n)] # _G. C. Greubel_, Mar 01 2019
%Y Cf. A003657.
%K nonn,easy,nice
%O 1,6
%A _N. J. A. Sloane_
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