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?

Submitted by Math Man

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Solution: (Hide)

19 since 1111111111111111111₁₉=109912203092239643840221 is prime.

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
re(3): Answer: for any composite, odd or even	Steve Herman	2013-07-25 09:31:14
re(2): Answer: for any composite, odd or even	Ady TZIDON	2013-07-24 15:36:40
re(2): Answer:	Steve Herman	2013-07-24 12:53:15
re: Answer:	Charlie	2013-07-24 12:42:29
computer solution	Charlie	2013-07-24 12:40:09
Answer:	broll	2013-07-24 11:29:46

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