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Expression Divisibility Decision (Posted on 2023-03-22) Difficulty: 3 of 5
Is mm-1 divisible by (m-1)2 for any integer value of m greater than 1.

Provide valid reasoning for your answer.

See The Solution Submitted by K Sengupta    
Rating: 5.0000 (1 votes)

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Solution Comment 1 of 1

m=2 is a trivial solution<o:p></o:p>

For m>2, m=integer, note that m and m-1 are always relatively prime.<o:p></o:p>

m^(m-1) = m * m * (m^(m-3)).  If this is to be divisible by (m-1)^2, then the last term must be divisible by (m-1)^2.  But the last term can then be written as m * m * (m^(m-5)).  Again the new last term must be devisable by (m-1)^2.  Follow this process to it’s logical end and you get two cases:<o:p></o:p>

1)      1) For m = odd, you get to m^(m-(m-2))= m^2, which is not divisible by (m-1)^2<o:p></o:p>

2)      2) For m = even, you get to m^1=m, which is also not divisible by (m-1)^2<o:p></o:p>

Therefore I believe m=2 is the only solution.<o:p></o:p>


  Posted by Kenny M on 2023-03-22 07:56:13
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