perplexus.info :: Numbers : Repunits and bases

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?

See The Solution Submitted by Math Man

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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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