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If I have k algebraic integers like a_1, ..., a_k such that the sum of their n-power are integer for n=1, ...m can we deduce that a_1, ..., a_k are integers? how large m should be? (how many power sum should be integers to deduce all a_i's are integers)

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closed as too localized by Gjergji Zaimi, Andreas Blass, Andrés E. Caicedo, Qiaochu Yuan, Dan Petersen Oct 25 '12 at 6:27

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Consider roots of unity. Gerhard "Ask Me About System Design" Paseman, 2012.10.24 – Gerhard Paseman Oct 25 '12 at 3:08
Look at Lucas numbers for example. $$(\frac{1-\sqrt{5}}{2})^n+(\frac{1+\sqrt{5}}{2})^n$$ is always an integer. – Gjergji Zaimi Oct 25 '12 at 3:09

A common theme to all comments and answers prior to this is the fact that if the algebraic integers you start with are closed under algebraic conjugation, then the power sums are all necessarily (by Galois theory) rational, so they are always (rational) integers, as rational algebraic integers are integers.

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Take any monic polynomial with integer coefficients and look at the roots.

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