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No n-th Powers Here! (Posted on 2005-09-05) |
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Show that the product of three consecutive positive integers cannot be the n-th power of an integer, for any integer n>1.
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Submitted by McWorter
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Rating: 3.4000 (5 votes)
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Solution:
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(Hide)
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(Proof by Claudio Buffara of Brazil) We may write the product as (m-1)m(m+1)=m(m^2-1). Suppose
m(m^2-1)=a^n, for some positive integer a and n>0.
Since m and m^2-1 are relatively prime, m must be an n-th power too. But then m^2 is also an n-th power. Hence two consecutive integers, m^2-1 and m^2, are n-th powers, with n>1. This contradicts the fact that consecutive n-th powers must differ by at least n ((x+1)^n=x^n+nx^(n-1)+more stuff). |
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