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What is the sum of the final three digits of the integer representation of $5^{100}$?

 Apr 5, 2021
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Nevermind, I got the answer, it is $13$, because for $5^n$, starting with $n=3$, we have the final digits as $125,625,125,625,125,625...$ and so on. Since $100$ is a multiple of $2$, it ends in $625$, and the sum of the digits is $\boxed{13}$

 Apr 5, 2021

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