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Power and Divisibility Puzzle (Posted on 2015-08-12) Difficulty: 3 of 5
Determine the total number of positive integer values of N < 20150 such that:
2N - N2 is divisible by 17

No Solution Yet Submitted by K Sengupta    
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Some Thoughts re: computer solution | Comment 2 of 6 |
(In reply to computer solution by Charlie)

It's not surprising that this can be readily solved by computer.  The challenge is to explain the result.

I would have guessed that 1/17 of the numbers would work, but 20149/17 ≈ 1185.235
but double this and you get 2370.47
so why do roughly 2/17 of numbers work?

Something interesting is going on.
I don't have time to investigate right now.

  Posted by Jer on 2015-08-12 22:29:12

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