1,1
Also numbers n such that (4*10^(n+1)+41)/9 is prime.
Index entries for primes involving repunits
Do[ If[ PrimeQ[40*(10^n - 1)/9 + 9], Print[n]], {n, 5000}]
Sequence in context: A126666 A154775 A167454 * A066684 A128124 A182687
Adjacent sequences: A056680 A056681 A056682 * A056684 A056685 A056686
hard,nonn
Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 10 2000