Continued fractions of certain Mahler functions

D. Badziahin

Abstract

We investigate the continued fraction expansion of the infinite products $g(x)=x^{-1}\prod _{t=0}^{\mathrm{\infty }}P(x^{-d^t})$ where polynomials $P(x)$ satisfy $P(0)=1$ and $\mathrm{deg}(P)<d$. We construct relations between partial quotients of $g(x)$ which can be used to get recurrent formulae for them. We provide that formulae for the cases $d=2$ and $d=3$. As an application, we prove that for $P(x)=1+ux$ where $u$ is an arbitrary rational number except 0 and 1, and for any integer $b$ with $|b|>1$ such that $g(b)\ne 0$ the irrationality exponent of $g(b)$ equals two. In the case $d=3$ we provide a partial analogue of the last result with several collections of polynomials $P(x)$ giving the irrationality exponent of $g(b)$ strictly bigger than two.

Keywords: Mahler function, Mahler number, irrationality exponent, continued fraction of Laurent series, Pade approximation.

AMS Subject Classification: Primary 11B83; secondary 11J82, 41A21.