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If you give me an integer N, how can I detect the nearest integer perfect power, larger or smaller than N?

In other words, the perfect power the distance between N and which is less than the distance between N and any other perfect power. Exponents of 1 are excluded. Prime or composite powers are ok.

This is not a homework question. Is there a method that is better than some kind of neighborhood door knock method? 'Hello, are you a perfect power? No, okay.'

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Or better than "Which of my n-th roots is closest to an integer?" –  User58220 Feb 8 '13 at 16:19
    
Exactly. Although @User58220 I think that would be optimal. I mean it is exactly O(log2 N) time, unless the nth root operation takes longer than this. So actually testing the deltas of the log2 N kth roots for k in 2 to log2 N. –  Cris Stringfellow Feb 9 '13 at 16:57
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