A014599 - OEIS

%I #13 May 15 2021 04:50:27

%S 1,1,1,2,1,3,1,3,2,4,1,5,2,4,3,4,1,7,2,5,3,6,2,8,2,5,3,8,2,10,2,5,5,6,

%T 3,10,2,7,4,10,1,11,4,6,5,8,2,13,4,9,4,6,3,14,4,7,5,12,2,15,3,6,7,12,

%U 4,13,2,11,4,12,3,14,4,8,8,10,3,19,4,10,4,12,3,18,6,7,5,12,4,19

%N Class numbers h(D) of imaginary quadratic fields with discriminant D=1-4*n.

%C Also class number, or number of equivalence classes of positive definite binary quadratic forms of discriminant -(4n-1). - _N. J. A. Sloane_, May 28 2014

%D D. A. Buell, Binary Quadratic Forms. Springer-Verlag, NY, 1989, pages 19 and 224-230. - _N. J. A. Sloane_, May 28 2014 [Only the squarefree cases appear on pp. 224-230]

%D H. Cohen, Course in Computational Alg. No. Theory, Springer, 1993, pp. 514-5.

%H N. J. A. Sloane, <a href="/A014599/b014599.txt">Table of n, a(n) for n = 1..10000</a>

%o (PARI) a(n) = qfbclassno(1-4*n)

%Y See A000003 for discriminant -4n.

%K nonn

%O 1,4

%A Eric Rains (rains(AT)caltech.edu)