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Scarce primes (Posted on 2011-01-10) Difficulty: 2 of 5
A repunit is a number consisting solely of ones (such as 11 or 11111).
Let us call p(n) a 10-base integer represented by a string of n ones, e.g. p(1)=1, p(5)=11111 etc.
Most of the repunit numbers are composite.
2, 19,23,317 are the first four indices of prime repunits.

Prove: For a prime repunit p(n) to be prime, n has to be prime.

No Solution Yet Submitted by Ady TZIDON    
Rating: 3.6667 (3 votes)

Comments: ( You must be logged in to post comments.)
  Subject Author Date
re(3): Another proofAdy TZIDON2011-01-14 02:40:36
re(2): Another proofGamer2011-01-11 14:16:32
Some Thoughtsre(3): proof, ok!Ady TZIDON2011-01-11 12:43:46
re(2): proofJer2011-01-11 10:18:20
Hints/Tipsre: Another proof - not a proofAdy TZIDON2011-01-11 02:10:16
SolutionproofPaul2011-01-10 22:23:15
Another proofGamer2011-01-10 18:45:40
Hints/Tipsre: proofAdy TZIDON2011-01-10 17:50:59
Hints/TipsRepunitsMath Man2011-01-10 17:40:22
proofJer2011-01-10 15:01:43
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