A100473 Numbers k such that 9*10^k + R_k + 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 17, 23, 73, 131, 473, 685, 701, 1909, 3029, 3473, 4193, 9931

Offset: 1

Author

Julien Peter Benney (jpbenney(AT)ftml.net), Nov 21 2004

Keywords

• more
• nonn

Comments

Also numbers k such that (82*10^k + 53)/9 is a prime.

Some of the larger entries may only correspond to probable primes.

a(14) > 10^5. - Robert Price, Oct 25 2015

Examples

			n = 1, 17, so that 97 and 911111111111111117 are primes.
		

Links

• Makoto Kamada, Prime numbers of the form 911...117.
• Index entries for primes involving repunits.

Crossrefs

Cf. A002275, A100999.

Programs

Mathematica

Do[ If[ PrimeQ[(82*10^n + 53)/9], Print[n]], {n, 0, 10000}] (* Robert G. Wilson v, Jan 19 2005 *)

Formula

a(n) = A100999(n) + 1.

Extensions

a(8)-a(12) from Robert G. Wilson v, Jan 12 2005

a(13) from Robert G. Wilson v, Jan 12 2005