A101393 Numbers k such that 3*10^k + R_k + 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 2, 218, 692, 1805, 2207, 2873, 59135

Offset: 1

Author

Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005

Keywords

• nonn

Comments

Also numbers k such that (28*10^k + 53)/9 is prime.

All except 1, 2 and 218 only probably prime. No others less than 10000.

Examples

			n = 1, 2 are members since 37 and 317 are primes.
		

Links

• Makoto Kamada, Prime numbers of the form 311...117.
• Index entries for primes involving repunits.

Crossrefs

Cf. A100501, A100473, A101826.

Programs

Mathematica

Do[ If[ PrimeQ[(28*10^n+53)/9], Print[n]], {n, 0, 10000}]

Formula

a(n) = A101826(n) + 1.

Extensions

a(8) from Kamada data by Robert Price, Dec 13 2010