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 \((a,r).\)

(第二十四届AIME1 2006 第9题)