A hidden signal in Hofstadter's $H$ sequence

TL;DR

This paper reveals a non-uniform distribution pattern in the scaled Hofstadter H sequence, linked to a specific algebraic number, and explores its connection to linear recurrence properties and distribution phenomena.

Contribution

It demonstrates that the scaled Hofstadter H sequence mod 1 converges to a non-uniform, possibly continuous but non-differentiable distribution, revealing new structure in this well-studied sequence.

Findings

The sequence $\alpha H(n) mod 1$ is not uniformly distributed.

The distribution appears to be continuous but not differentiable.

A connection is established between this distribution and linear recurrence properties.

Abstract

The Hofstadter $H$ sequence is defined by $H(1) = 1$ and $H(n) = n-H(H(H(n-1)))$ for $n > 1$. If $\alpha$ is the real root of $x^3+x=1$ we show that the numbers $\alpha H(n) \mod 1$ are not uniformly distributed on $[0,1]$, but converge to a distribution we believe is continuous but not differentiable. This is motivated by a discovery of Steinerberger, who found a real number with similar behavior for the Ulam sequence. Our result is related with the fact that a certain sequence defined from the linear recurrence $h_n=h_{n-1}+h_{n-3}$ has the property $\|x h_n\| \rightarrow 0$ precisely for $x \in \mathbb{Z}[\alpha]$, a phenomenon we inquire for general linear recurrent sequences of integers.