## a3r

## repunit

A reepunit is an integer of the form R_{n}=(10^{n}-1)/9.
It consists of n copies of the digit 1 in decimal representation.
R_{n} is proved to be prime for n=2,19,23,317,1031. R_{49081} and R_{86453} are probably prime.
It has been conjectured that there are infinitely many repunit primes.