Let $D$ be a common denominator of the rational numbers $a_1, \ldots, a_r$ and let $A = \max(1, |a_1|, \ldots, |a_r|)$. Show that $D^n u_n \in \mathbf{Z}$ for all $n \geq 0$.
Let $D$ be a common denominator of the rational numbers $a_1, \ldots, a_r$ and let $A = \max(1, |a_1|, \ldots, |a_r|)$. Show that $D^n u_n \in \mathbf{Z}$ for all $n \geq 0$.