English

Continued fraction digit averages an Maclaurin's inequalities

Number Theory 2014-07-30 v3 Classical Analysis and ODEs Dynamical Systems

Abstract

A classical result of Khinchin says that for almost all real numbers α\alpha, the geometric mean of the first nn digits ai(α)a_i(\alpha) in the continued fraction expansion of α\alpha converges to a number K=2.6854520K = 2.6854520\ldots (Khinchin's constant) as nn \to \infty. On the other hand, for almost all α\alpha, the arithmetic mean of the first nn continued fraction digits ai(α)a_i(\alpha) approaches infinity as nn \to \infty. There is a sequence of refinements of the AM-GM inequality, Maclaurin's inequalities, relating the 1/k1/k-th powers of the kk-th elementary symmetric means of nn numbers for 1kn1 \leq k \leq n. On the left end (when k=nk=n) we have the geometric mean, and on the right end (k=1k=1) we have the arithmetic mean. We analyze what happens to the means of continued fraction digits of a typical real number in the limit as one moves f(n)f(n) steps away from either extreme. We prove sufficient conditions on f(n)f(n) to ensure to ensure divergence when one moves f(n)f(n) steps away from the arithmetic mean and convergence when one moves f(n)f(n) steps away from the geometric mean. For typical α\alpha we conjecture the behavior for f(n)=cnf(n)=cn, 0<c<10<c<1. We also study the limiting behavior of such means for quadratic irrational α\alpha, providing rigorous results, as well as numerically supported conjectures.

Keywords

Cite

@article{arxiv.1402.0208,
  title  = {Continued fraction digit averages an Maclaurin's inequalities},
  author = {Francesco Cellarosi and Doug Hensley and Steven J. Miller and Jake L. Wellens},
  journal= {arXiv preprint arXiv:1402.0208},
  year   = {2014}
}

Comments

32 pages, 7 figures. Substantial additions were made to previous version, including Theorem 1.3, Section 6, and Appendix A