We define a subset $\mathcal Z$ of $(1,+\infty)$ with the property that for each $\alpha \in {\mathcal Z}$ there is a nonzero real number $\xi = \xi(\alpha)$ such that the integral parts $[\xi \alpha^n]$ are even for all $n \in \mathbb{N}$. A result of Tijdeman implies that each number greater than or equal to 3 belongs to $\mathcal{Z}$. However, Mahler's question on whether the number 3/2 belongs to $\mathcal{Z}$ or not remains open. We prove that the set ${\mathcal S}:=(1,+\infty) \textbackslash {\mathcal Z}$ is nonempty and find explicitly some numbers in ${\mathcal Z} \cap$ (5/4,3) and in ${\mathcal S} \cap (1,2)$.