On the variance of the digits of $1/p$

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Authors: Kurt Girstmair
Cited by: 0

Abstract

Let $p>3$ be a prime and $b\ge 2$ an integer such that $p$ does not divide $b$. Then $1/p$ has a periodic digit expansion with respect to the basis $b$. The length $q$ of the period is the (multiplicative) order of $b$ mod $p$. In the case $q=p-1$ a formula for the variance of the digits of a period was given previously. This formula involves a Dedekind sum. We determine the variance in the case $q=(p-1)/2$. If $p\equiv 3$ mod 4 a Dedekind sum and the class number of $\mathbb Q(\sqrt{-p})$ occur in the respective formula. If $p\equiv 1$ mod 4, the formula may be much more complex since it involves linear combinations of (possibly many) products of two Bernoulli numbers attached to odd characters.

Fields of Study & Subjects

Analytic Number Theory Research Advanced Mathematical Identities Algebraic Geometry and Number Theory

Publication details

Journal / source
arXiv (Cornell University)
Publication date
13 January 2026
Document type
Preprint