23

This number is a prime.

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23 is the only known number p where Rp is a repunit prime, 10^p-p is prime, and p is a prime factor of a Mersenne number with repunit exponent. I.e., 23 is factor of 2^11-1. [Luhn]

Submitted: 2004-09-08 14:50:46;   Last Modified: 2012-06-06 12:08:05.
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