"Robert G. Wilson v" wrote:
> Yes it is. In fact there are five numbers with this
> characteristic. (10^n -1)/9 is prime when n is 2, 19, 23, 317 & 1031.
> See "The Encyclopedia of Integer Sequences" sequence M2114, Neil J.A.
> Sloane and Simon Plouffe, Academic Press, 1995.
>
Are all others proved composite, or are the bigger ones merely beyond the
current limit of primalty testing?
Ciao,
Alex.
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