TR-MO 2001 Problem 2

$(x_{n})_{-\infty<n<\infty}$ is a sequence of real numbers which satisfies $x_{n+1}=\frac{x_{n}^2+10}{7}$ for every $n \in \mathbb{Z}$ . If there exist a real upperbound for this sequence, find all the values $x_{0}$ can take.