9. As shown in the figure, the two sides of $\angle A O B$ have $n(n>1)$ points $A_{1}, A_{2}, A_{3}, \cdots \cdots, A_{n}$ and $B_{1}, B_{2}$, $B_{3}, \cdots \cdots, B_{n}$, respectively. It is known that $O A_{1}=A_{1} B_{2}=B_{2} A_{3}=\cdots=A_{n} B_{n}=\cdots=B_{3} A_{2}=A_{2} B_{1}=B_{1} O$, and the degree of $\angle A O B$ is an integer. Then the number of possible values for $\angle A O B$ is $\qquad$.
$4$