A102992 Numbers n such that 4*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 2, 4, 5, 13, 22, 25, 28, 38, 67, 142, 284, 295, 380, 397, 1217, 1640, 2885, 3286, 7735, 29306

Offset: 1

Author

Robert G. Wilson v, Jan 17 2005

Keywords

• more
• nonn

Comments

Also numbers n such that (41*10^n+13)/9 is prime.

a(22) > 10^5. - Robert Price, May 22 2015

Links

• Makoto Kamada, Prime numbers of the form 455...557.
• Index entries for primes involving repunits.

Crossrefs

Cf. A002275, A101727.

Programs

Mathematica

Do[ If[ PrimeQ[(41*10^n + 13)/9], Print[n]], {n, 0, 10000}]

Formula

a(n) = A101727(n) + 1.

Extensions

Addition of a(21) from Kamada data by Robert Price, Dec 09 2010