The number of positive integers $ n=2^a3^b$ such that $n^6$ does not divide $6^n$

Question

$6^n=(2\cdot3)^n$ is not divisible by $n^6$ So we have to find those numbers which does not divide 6 and also expressed by the prime factors of 2 and 3 but after this I am getting no way to proceed .

Answer 1

Hint: If $n = 2^a 3^b$, $n^6 = 2^{6a} 3^{6b}$. What must be true for this not to divide $2^n 3^n$?