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Perfect Square To Divisibility By 56 (Posted on 2010-04-01) Difficulty: 4 of 5
N is a positive integer such that each of 3*N + 1 and 4*N + 1 is a perfect square.

Is N always divisible by 56?

If so, prove it. Otherwise, give a counterexample.

See The Solution Submitted by K Sengupta    
Rating: 4.0000 (1 votes)

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re: Does this explain why 7 is a factor of n? | Comment 13 of 14 |
(In reply to Does this explain why 7 is a factor of n? by broll)

Unfortunately it does not.

In steps 3 and 4 all you really did was introduce variables k and l (the x and y seem irrelevant.)

In steps 5 and 6 you prove that (k+l) is divisible by 7.  For instance if n=3, (k+l)=21.

  Posted by Jer on 2010-04-06 10:18:02

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