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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>1 is the n-th fundamental discriminant.
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%I #9 Dec 14 2019 21:32:08

%S 1,1,2,1,1,2,2,2,1,2,1,2,1,2,1,2,2,4,1,2,2,1,2,2,2,2,1,2,2,1,1,2,4,1,

%T 1,4,2,2,2,3,1,4,2,3,1,2,4,1,2,4,4,2,1,2,1,2,2,2,1

%N 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>1 is the n-th fundamental discriminant.

%C A003646 is the same except it is under the action of SL_2[Z].

%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 Jens Jonasson, <a href="http://www.mai.liu.se/~jejon/">Classes of integral binary quadratic forms</a>, Master's thesis (2001), Appendix B.

%e D = 5, 8, 12, 13, 17, 21, 24, 28, ..., that is, A003658.

%Y Cf. A003658, A003646.

%K nonn

%O 1,3

%A _Steven Finch_, May 05 2005