1,2

Also numbers n such that 5*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

Makoto Kamada, Factorizations of 599...993.

Index entries for primes involving repunits.

Do[ If[ PrimeQ[6*10^n - 7], Print[n]], {n, 0, 10000}]

Sequence in context: A043329 A023699 A058605 this_sequence A134080 A111300 A117548

Adjacent sequences: A103022 A103023 A103024 this_sequence A103026 A103027 A103028

more,nonn

Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 18 2005