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Repunits and bases (
Posted on 20130724
)
11
_{2}
=3 and 111
_{3}
=13 are prime. However, 1111
_{4}
=85=5*17 and 11111
_{5}
=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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Submitted by
Math Man
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re(2): Answer:
 Comment 4 of 6 
(In reply to
re: Answer:
by Charlie)
Good question, Charlie!
It is obvious to me that only odd values of n need to be checked.
If n = 2k, then
((2k)^(2k))1 can be factored into
(
((2k)^(k))1) *
(
((2k)^(k))+1),
and x is not going to be prime if k > 1
Posted by
Steve Herman
on 20130724 12:53:15
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