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How Many ? (Posted on 2004-01-02) Difficulty: 3 of 5
How many positive integers 'n' are there such that [(2)^n + 1] is divisible by 7 ?

See The Solution Submitted by Ravi Raja    
Rating: 2.6667 (9 votes)

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re: la meme Janette mais autrement coifee! | Comment 5 of 6 |
(In reply to la meme Janette mais autrement coifee! by luminita)

An unusual approach, but I don't think its valid. For the first term, k*2^3 is even regardless of k; so if k is odd, both the first and second term are even, resulting in an even value for the right side. So it is possible to have an even value for the right side (of your second equation). What you need to show is the right side cannot be a multiple of 2, a harder task.
  Posted by mark hartman on 2004-01-29 18:42:49

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