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JOURNALS // Zapiski Nauchnykh Seminarov POMI // Archive

Zap. Nauchn. Sem. POMI, 2001 Volume 276, Pages 312–333 (Mi znsl1424)

This article is cited in 1 paper

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


 English version:
Journal of Mathematical Sciences (New York), 2003, 118:1, 4918–4932

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