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 Scarce primes (Posted on 2011-01-10)
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)

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 Subject Author Date re(3): Another proof Ady TZIDON 2011-01-14 02:40:36 re(2): Another proof Gamer 2011-01-11 14:16:32 re(3): proof, ok! Ady TZIDON 2011-01-11 12:43:46 re(2): proof Jer 2011-01-11 10:18:20 re: Another proof - not a proof Ady TZIDON 2011-01-11 02:10:16 proof Paul 2011-01-10 22:23:15 Another proof Gamer 2011-01-10 18:45:40 re: proof Ady TZIDON 2011-01-10 17:50:59 Repunits Math Man 2011-01-10 17:40:22 proof Jer 2011-01-10 15:01:43

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