The mean relative maximum of Collatz trajectories

For the ordinary Collatz map C(n)=n/2 for even n and C(n)=3n+1 for odd n, let H(n)=sup over j>=0 of C^j(n), allowing positive infinity. This self-contained note proves that liminf as N tends to infinity of (1/(N log N)) times the sum over 1<=n<=N of H(n)/n is at least log(27/16)/(6 log(2) log(3/2)), which is positive. The same lower bound is already witnessed by maxima over an explicitly logarithmic number of iterations. Those finite-horizon summands are always finite, so the argument needs neither an infinite summand nor the Collatz conjecture. In particular, the mean relative maximum tends to infinity, giving a quantitative answer to Jarvis's question about a finite mean limit. The proof combines classical exact finite parity coding with a finite entropy estimate that charges logarithmic growth to increases of the running maximum. Background on converse maximal inequalities and the scalar estimate is credited to Gundy and Sason-Verdu. No claim of first historical priority, an optimal Collatz coefficient, a matching asymptotic, or a proof of Collatz convergence is made. This is a preprint prepared with AI assistance; it has not undergone external journal peer review.

Authors

Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-10-17
DOI
https://doi.org/10.5281/zenodo.23429554
Primary Topic
Mathematical Dynamics and Fractals
Type
preprint
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preprint

The mean relative maximum of Collatz trajectories

David Leen
Zenodo (CERN European Organization for Nuclear Research)
Mathematical Dynamics and Fractals
preprint

The mean relative maximum of Collatz trajectories

David Leen
preprint en

Abstract

For the ordinary Collatz map C(n)=n/2 for even n and C(n)=3n+1 for odd n, let H(n)=sup over j>=0 of C^j(n), allowing positive infinity. This self-contained note proves that liminf as N tends to infinity of (1/(N log N)) times the sum over 1<=n<=N of H(n)/n is at least log(27/16)/(6 log(2) log(3/2)), which is positive. The same lower bound is already witnessed by maxima over an explicitly logarithmic number of iterations. Those finite-horizon summands are always finite, so the argument needs neither an infinite summand nor the Collatz conjecture. In particular, the mean relative maximum tends to infinity, giving a quantitative answer to Jarvis's question about a finite mean limit. The proof combines classical exact finite parity coding with a finite entropy estimate that charges logarithmic growth to increases of the running maximum. Background on converse maximal inequalities and the scalar estimate is credited to Gundy and Sason-Verdu. No claim of first historical priority, an optimal Collatz coefficient, a matching asymptotic, or a proof of Collatz convergence is made. This is a preprint prepared with AI assistance; it has not undergone external journal peer review.

Zenodo (CERN European Organization for Nuclear Research)
Mathematical Dynamics and Fractals
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