SMO 2008 Senior Round 1 Question 35

Let $a_1,a_2,a_3,\ldots$ be all positive integers relatively prime to $75$, in increasing order. The first five terms are $a_1=1$, $a_2=2$, $a_3=4$, $a_4=7$, $a_5=8$. Find $a_{2008}$.