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Composite? Yes. (Posted on 2010-08-24) Difficulty: 3 of 5
Prove that (258+1)/5 is a composite number.

No Solution Yet Submitted by Ady TZIDON    
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Hints/Tips another approach | Comment 2 of 3 |

The factorisation 2^(4n+2)+1 = [2^(2n+1)-2^(n+1)+1]*[(2^2n+1)+2^(n+1)+1] suggests to me that not only is the expression  divisible by 5, but also that every prime factor of the expression is itself a prime of the form 4k+1, or a power of such a number.

  Posted by broll on 2010-08-25 07:23:41
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