1989 IMO Problems/Problem 5
Prove that for each positive integer there exist consecutive positive integers none of which is an integral power of a prime number.
There are at most 'true' powers in the set . So when gives the amount of 'true' powers we get that .
Since also , we get that . Now assume that there is no 'gap' of lenght at least into the set of 'true' powers and the primes. Then this would give that for all in contrary to the above (at east this proves a bit more).
Edit: to elementarize the part: Look . Then all numbers in the residue classes are not primes (except the smallest representants sometimes). So when there wouldn't exist a gap of length , there has to be a 'true' power in each of these gaps of the prime numbers, so at least one power each numbers, again contradicting .
This solution was posted and copyrighted by ZetaX. The original thread for this problem can be found here: 
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