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Class numbers of indefinite binary quadratic forms
O. M. Fomenko St. Petersburg Department of V. A. Steklov Institute of Mathematics, Russian Academy of Sciences
Abstract:
Let
$h(d)$ be the class number of properly equivalent primitive binary quadratic forms
$ax^2+bxy+cy^2$ of discriminant
$d=b^2-4ac$. The case of indefinite forms
$(d<0)$ is considered.
Assuming that the extended Riemann hypothesis for some fields of algebraic numbers holds, the following results are proved.
1. Let
$\alpha(x)$ be an arbitrarily slow monotonically increasing function such that
$\alpha(x)\to\infty$. Then
$$
\#\biggl\{p\le x\bigg\vert\biggl(\frac5p\biggr)=1,\,h(5p^2)>(\log p)^{\alpha(p)}\biggr\}=o(\pi(x)),
$$
where
$\pi(x)=\#\{p\le x\}$.
2. Let
$F$ be an arbitrary sufficiently large positive constant. Then for
$x>x_F$ , the relation
$$
\#\biggl\{p\le x\bigg\vert\biggl(\frac 5p\biggr)=1,\,h(5p^2)>F\biggr\}\asymp\frac{\pi(x)}F
$$
holds.
3. The relation
$$
\#\biggl\{p\le x\bigg\vert\biggl(\frac5p\biggr)=1,\,h(5p^2)=2\biggr\}\sim\frac9{19}A\pi(x)
$$
holds, where
$A$ is Artin's constant.
Hence, for the majority of discriminants of the form
$d=5p^2$, where
$\bigl(\frac 5p\bigr)=1$, the class numbers are small. This is consistent with the Gauss conjecture concerning the behavior of
$h(d)$ for the majority of discriminants
$d>0$ in the general case.
UDC:
511.466+517.863
Received: 26.03.2001