The full question is:
Find the number of digits, $D$, in the decimal expansion of the large number
$$N=4^{4^{4^{4}}}$$
Try and find the most efficient ways of finding $D$.
I know that $4^{4^{4^{4}}}$ computes a very large number i.e. $4^{4^{256}}$. I'm not sure how to go about working out both the decimal expansion and finding the number of digits $D$ in the question. Please can someone kindly help! thank you