# how to find the most significant three digits of N to the power M?

$N$ can be at most $10^{10}$ and $M$ can be at most $10^7$. How can I find the first three digits of $N^M$ ?

Is there an easy way to find this like the process of finding last digit ?

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If $N$ and $M$ are so small, you might as well just calculate $N^M$ rather than waste time thinking of a smarter method. – Chris Eagle Nov 1 '12 at 11:52
what if they are very large ? – johnsmith Nov 1 '12 at 12:00

If $X = N^M$, compute $z = 3 + (\log_{10} X \mod 1)$ and then round $y = 10^z$ down to the next integer. This should work for $X \ge 10^3$ and should give a correct answer in IEEE arithmetic for the desired range of $N$ and $M$. For smaller X$, just compute it directly. - Is not$(\log_{10} X \mod 1)$always zero? or you use mod with a different meaning? And$10^z$is always a multiple of 10, that can't be most significant 3 digits of any$N^M$– sowrov May 21 '13 at 9:50$\log_{10} X \mod 1$is the fractional part of$\log_{10} X$. – Hans Engler May 21 '13 at 17:37 So, I suppose that in the place of 3 it can be any number between 1 and$M*\lceil \log_{10}X \rceil\$ – xpy Jan 26 '14 at 14:50