1,2

Also numbers n such that 4*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

Makoto Kamada, Factorizations of 499...993.

Index entries for primes involving repunits.

Do[ If[ PrimeQ[5*10^n - 7], Print[n]], {n, 0, 10000}]

Adjacent sequences: A102999 A103000 A103001 this_sequence A103003 A103004 A103005

Sequence in context: A121980 A091231 A049893 this_sequence A004979 A051788 A023623

more,nonn

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