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 Repunits and bases (Posted on 2013-07-24)
112=3 and 1113=13 are prime. However, 11114=85=5*17 and 111115=781=11*71 are not prime. What is the least number n>3 such that the repunit consisting of n 1's in base n is prime?

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 re(3): Answer: for any composite, odd or even Comment 6 of 6 |
(In reply to re(2): Answer: for any composite, odd or even by Ady TZIDON)

Oh.  Now that it has been pointed out, it is both clever and obvious.

Thanks, Ady!

 Posted by Steve Herman on 2013-07-25 09:31:14
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