A103091 Numbers n such that 8*10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 3, 6, 31, 36, 61, 117, 229, 339, 3165, 3958, 5277, 5343, 6079, 6535, 8485, 15084, 34537

Offset: 1

Author

Robert G. Wilson v, Jan 19 2005

Keywords

• more
• nonn

Comments

Also numbers n such that (79*10^n+11)/9 is prime.

a(19) > 10^5. - Robert Price, Oct 27 2015

Links

• Makoto Kamada, Prime numbers of the form 877...779.
• Index entries for primes involving repunits.

Crossrefs

Cf. A002275, A101078.

Programs

Mathematica

Do[ If[ PrimeQ[(79*10^n + 11)/9], Print[n]], {n, 0, 10000}]

Formula

a(n) = A101078(n) + 1.

Extensions

a(17) from Kamada data by Robert Price, Dec 14 2010

a(18) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013