1,3

Also numbers n such that (4*10^(n+1)+23)/9 is prime.

Index entries for primes involving repunits

Do[ If[ PrimeQ[40*(10^n - 1)/9 + 7], Print[n]], {n, 0, 5000}]

Sequence in context: A084670 A002091 A056259 this_sequence A032670 A068677 A069832

Adjacent sequences: A056679 A056680 A056681 this_sequence A056683 A056684 A056685

hard,nonn

Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 10 2000