A102935 Numbers k such that 10^k + 4*R_k + 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 2, 4, 11, 13, 26, 154, 196, 436, 529, 1111, 2563, 2641, 3233, 3883, 4256, 9298, 17293, 23270, 27197, 129826

Offset: 1

Author

Robert G. Wilson v, Dec 16 2004

Keywords

• more
• nonn

Comments

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

a(21) > 10^5. - Robert Price, Apr 19 2015

Links

• Makoto Kamada, Prime numbers of the form 144...449.
• Index entries for primes involving repunits.

Crossrefs

Cf. A002275, A102017.

Programs

Mathematica

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

Formula

a(n) = A102017(n) + 1.

Extensions

a(18)-a(20) from Kamada data by Robert Price, Dec 09 2010

a(21) from Kamada data by Tyler Busby, Apr 14 2024