Generalized $k$-regular sequences III: Arithmetical properties of generalized $k$-regular series

Abstract

Let $F(z)$ be a $k$-regular series in $\mathbb{Z}[[z]]$ and $b$ be an integer with $b\ge2$. Bell, Bugeaud and Coons [BelBC] proved that $F(\frac{1}{b})$ is either rational or transcendental. In [Mi], we introduce a generalized $k$-regular sequence as a unification of several kinds of important sequences including $k$-regular, $k$-additive and $k$-multiplicative sequences. In this paper, we give a generalization of the result of Bell, Bugeaud and Coons for certain generalized $k$-regular series. Especially, we show that the values of irrational generating functions of certain sum of $k$-additive sequences and certain $k$-multiplicative sequences are either rational or transcendental. Moreover, we also give a partly generalization of a result obtained by Tachiya[Ta]. Especially, we show that the values of irrational generating functions of certain $k$-additive sequences and certain $k$-multiplicative sequences give transcendental numbers.