If $\log_2(\log_2(\log_2(x)))=2$, then how many digits are in the base-ten representation for x?
$\text{(A) } 5\quad \text{(B) } 7\quad \text{(C) } 9\quad \text{(D) } 11\quad \text{(E) } 13$
Taking successive exponentials $\log_2(\log_2(x)) = 2^2 = 4$ and $\log_2(x) = 2^4=16$ and $x = 2^{16}$.  Now $2^{10} = 1024 \approx 10^3$ and $2^6 = 64$ so we can approximate $2^{16} \approx 64000$ which has 5 digits.  In general, $2^n$ has approximately $n/3$ digits.
$\fbox{A}$