\[\frac{n + 9}{n} = \frac{n}{n} + \frac{9}{n} = 1 + \frac{9}{n}\]
\[\left( 1 + \frac{9}{n} \right) \in Z,\ если\ n =\]
\[= - 9; - 3;\ - 1;1;3;9.\]