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A106031 a(n) is the number of orbits under the action of GL_2[Z] on the primitive binary quadratic forms of discriminant D, where D < 0 is the n-th fundamental discriminant.

%I A106031 #9 Dec 14 2019 21:32:39
%S A106031 1,1,1,1,1,2,1,2,2,2,2,2,3,2,1,3,2,2,3,3,2,1,3,4,3,2,4,4,2,2,5,3,4,2,
%T A106031 5,2,4,6,4,2,3,3,4,3,2,6,2,4,4,3,6,1,5,6,4,3,5,3,2,7
%N A106031 a(n) is the number of orbits under the action of GL_2[Z] on the primitive binary quadratic forms of discriminant D, where D < 0 is the n-th fundamental discriminant.
%C A106031 A006641 is the same except it is under the action of SL_2[Z].
%H A106031 S. R. Finch, <a href="http://www.people.fas.harvard.edu/~sfinch/">Class number theory</a>
%H A106031 Steven R. Finch, <a href="/A000924/a000924.pdf">Class number theory</a> [Cached copy, with permission of the author]
%H A106031 Jens Jonasson, <a href="http://www.mai.liu.se/~jejon/">Classes of integral binary quadratic forms</a>, Master's thesis (2001), Appendix B.
%e A106031 D = -3, -4, -7, -8, -11, -15, -19, -20, -23, -24, -31, ...,
%e A106031 that is, A003657 negated.
%Y A106031 Cf. A003657, A006641.
%K A106031 nonn
%O A106031 1,6
%A A106031 _Steven Finch_, May 05 2005