Transcendence results on the generating functions of the characteristic functions of certain self-generating sets

Tom 162 / 2014

Peter Bundschuh, Keijo Väänänen Acta Arithmetica 162 (2014), 273-288 MSC: Primary 11J81; Secondary 11J82, 11J91, 30B30. DOI: 10.4064/aa162-3-5


This article continues two papers which recently appeared in this same journal. First, Dilcher and Stolarsky [140 (2009)] introduced two new power series, $F(z)$ and $G(z)$, related to the so-called Stern polynomials and having coefficients 0 and 1 only. Shortly later, Adamczewski [142 (2010)] proved, inter alia, that $G(\alpha ),G(\alpha ^4)$ are algebraically independent for any algebraic $\alpha $ with $0<|\alpha |<1$. \par Our first key result is that $F$ and $G$ have large blocks of consecutive zero coefficients. Then, a Roth-type argument shows that $F(a/b)$ and $G(a/b)$, for any $(a,b)\in \mathbb {Z}\times \mathbb {N}$ with $0<|a|<\sqrt {b}$, are transcendental but not U-numbers. Moreover, reasonably good upper bounds for the irrationality exponent of these numbers are obtained. Another main result for which an elementary (or poor men's) proof is presented concerns the algebraic independence of $F(z),F(z^4)$ over $\mathbb {C}(z)$ leading to the $F$-analogue of Adamczewski's above-mentioned theorem.


  • Peter BundschuhMathematisches Institut
    Universität zu Köln
    Weyertal 86-90
    50931 Köln, Germany
  • Keijo VäänänenDepartment of Mathematical Sciences
    University of Oulu
    P.O. Box 3000
    90014 Oulu, Finland

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