1,2

Also numbers n such that (2*10^(n+1)+61)/9 is prime.

Index entries for primes involving repunits

Makoto Kamada, Factorizations of 22...229.

Do[ If[ PrimeQ[20*(10^n - 1)/9 + 9], Print[n]], {n, 5000}]

Cf. A093401 (corresponding primes).

Sequence in context: A103845 A055463 A091957 this_sequence A092665 A131758 A095909

Adjacent sequences: A056675 A056676 A056677 this_sequence A056679 A056680 A056681

hard,nonn

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

Two more terms from Rick L. Shepherd (rshepherd2(AT)hotmail.com), Mar 30 2004

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