A102989 Numbers n such that 4*10^n + 3*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 3, 5, 6, 8, 15, 26, 53, 60, 97, 183, 205, 302, 396, 456, 467, 607, 828, 1860, 2743, 4273, 4781, 5712, 6038, 6637, 9222, 10832, 18865, 25848, 42247, 48547, 87565, 95588

Offset: 1

Author

Robert G. Wilson v, Jan 17 2005

Keywords

• more
• nonn

Comments

Also numbers n such that (13*10^n+11)/3 is prime.

a(34) > 10^5. - Robert Price, May 11 2015

Links

• Makoto Kamada, Prime numbers of the form 433...337.
• Index entries for primes involving repunits.

Crossrefs

Cf. A002275, A101724.

Programs

Mathematica

Do[ If[ PrimeQ[(13*10^n + 11)/3], Print[n]], {n, 0, 10000}]

Formula

a(n) = A101724(n) + 1.

Extensions

Addition of a(27)-a(29) from Kamada data by Robert Price, Dec 08 2010

a(30)-a(31) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013

a(32)-a(33) from Robert Price, May 11 2015