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All/Any different? (Posted on 2005-08-16) Difficulty: 4 of 5
Given positive integer n, consider the set of numbers {n²+1, n²+2, ... (n+1)²}. If we pick two numbers x and y out of that set, how many different values can the product xy take?

See The Solution Submitted by Federico Kereki    
Rating: 3.5000 (6 votes)

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re(3): Where's the proof? | Comment 25 of 27 |
(In reply to re(2): Where's the proof? by Josh70679)

Sorry, Josh.  I got lost in the thicket of comments and didn't realize you had sketched a proof of the crucial point.  The easily calculated number n(2n+1) counts for little without the proof that the products are distinct.  I do think that your use of the gcds can be avoided, but this isn't really important.
  Posted by Richard on 2005-08-20 09:30:09

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