Let a_{1}, a_{2}, \ldots be a sequence of integers determined by the rule a_{n}=a_{n-1} / 2 if a_{n-1} is even and a_{n}=3 a_{n-1}+1 if a_{n-1} is odd. For how many positive integers a_{1} \leq 2008 is it true that a_{1} is less than each of a_{2}, a_{3}, and a_{4} ?
Answer Choices
A. 250
B. 251
C. 501
D. 502
E. 1004