1,2

Also numbers n such that 4*10^n + 9*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

Makoto Kamada, Factorizations of 499...997.

Index entries for primes involving repunits.

Do[ If[ PrimeQ[5*10^n - 3], Print[n]], {n, 0, 10000}]

Sequence in context: A068020 A131991 A116042 this_sequence A024845 A056698 A070007

Adjacent sequences: A103000 A103001 A103002 this_sequence A103004 A103005 A103006

more,nonn

Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 17 2005