1,2

Also numbers n such that (43*10^n-7)/9 is prime.

Makoto Kamada, Factorizations of 477...77

Index entries for primes involving repunits

Do[ If[ PrimeQ[ 4*10^n + 7*(10^n-1)/9], Print[n]], {n, 0, 6000}]

Sequence in context: A085018 A001741 A154820 this_sequence A092484 A091823 A024834

Adjacent sequences: A056705 A056706 A056707 this_sequence A056709 A056710 A056711

hard,nonn

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

8274 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008