1,3

Also numbers n such that 10^(n+1) - 3 is a prime number.

Index entries for primes involving repunits

Makoto Kamada, Factorizations of 99...997.

Do[ If[ PrimeQ[ 90*(10^n - 1)/9 + 7 ], Print[n]], {n, 0, 1250}]

Sequence in context: A001252 A067058 A002302 this_sequence A151402 A003768 A024915

Adjacent sequences: A056659 A056660 A056661 this_sequence A056663 A056664 A056665

hard,nonn

Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 09 2000

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