A103067 Numbers k such that 7*10^k + 8*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 4, 18, 28, 55, 1728, 1876, 1884, 6841, 10782, 25366, 98446, 137250

Offset: 1

Author

Robert G. Wilson v, Jan 19 2005

Keywords

• more
• nonn

Comments

Also numbers k such that (71*10^k+1)/9 is prime.

Links

• Makoto Kamada, Prime numbers of the form 788...889.
• Index entries for primes involving repunits.

Crossrefs

Cf. A002275, A101153.

Programs

Mathematica

Do[ If[ PrimeQ[(71*10^n + 1)/9], Print[n]], {n, 0, 10000}]

Formula

a(n) = A101153(n) + 1.

Extensions

a(10)-a(13) from Kamada data by Robert Price, Dec 14 2010