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No n-th Powers Here! (Posted on 2005-09-05) Difficulty: 3 of 5
Show that the product of three consecutive positive integers cannot be the n-th power of an integer, for any integer n>1.

  Submitted by McWorter    
Rating: 3.4000 (5 votes)
Solution: (Hide)
(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).

Comments: ( You must be logged in to post comments.)
  Subject Author Date
My SolutionChristie2005-09-20 20:58:36
SolutionsolutiongoFish2005-09-14 09:11:17
re(3): Solution?McWorter2005-09-05 22:04:49
Hmmm...Dan2005-09-05 21:37:02
re(2): Solution?Tan Kiat Chuan2005-09-05 17:55:50
Some Thoughtsre: Solution?Old Original Oskar!2005-09-05 15:03:53
SolutionSolution?Tan Kiat Chuan2005-09-05 14:55:00
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