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Calculate $1^{30} + 2^{30} + 3^{30} + \ldots + 17^{30} \mod 31$

Using Fermat's Theorem: $$ 1^{30} = 1 \mod 31, $$ (since $31$ is prime). This implies the above is congruent to $17 \mod 31$

This is correct, right?

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I think you have a typo in your solution: $1^{30} = 1$ (mod $31$), while true, is not what you meant to say (i.e. you need this fact for all the other 30th powers too). [See the answers below.] –  Matt E Oct 18 '10 at 15:24

1 Answer 1

up vote 6 down vote accepted

True. But 1^n=1 mod whatever. Fermat's Little Theorem says that n^30=1 for all n prime to 31. So your answer of 17 is correct.

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