2006 AIME I Problem 9

The sequence a_{1}, a_{2}, \ldots is geometric with a_{1}=a and common ratio r, where a and r are positive integers. Given that \log _{8} a_{1}+\log _{8} a_{2}+\cdots+\log _{8} a_{12}=2006, find the number of possible ordered pairs (a, r).