A102994 Numbers n such that 4*10^n + 6*R_n - 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 2, 7, 9, 14, 24, 45, 49, 73, 74, 232, 338, 397, 504, 1063, 2817, 5305, 16768, 27060

Offset: 1

Author

Robert G. Wilson v, Jan 17 2005

Keywords

• more
• nonn

Comments

Also numbers n such that (14*10^n-17)/3 is prime.

a(20) > 10^5. - Robert Price, May 27 2015

Links

• Makoto Kamada, Prime numbers of the form 466...661.
• Index entries for primes involving repunits.

Crossrefs

Cf. A002275, A101729.

Programs

Mathematica

Do[ If[ PrimeQ[(14*10^n - 17)/3], Print[n]], {n, 0, 10000}]

Formula

a(n) = A101729(n) + 1.

Extensions

Addition of a(18)-a(19) from Kamada data by Robert Price, Dec 10 2010