A103060 Numbers n such that 7*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 2, 5, 7, 23, 32, 38, 47, 116, 140, 229, 247, 734, 931, 1346, 2162, 2546, 6980, 10283, 10543, 12128, 13741, 105320

Offset

1,2

Comments

Also numbers n such that (68*10^n-41)/9 is prime.

Links

Table of n, a(n) for n=1..23.

Makoto Kamada, Prime numbers of the form 755...551.

Index entries for primes involving repunits.

Formula

a(n) = A101143(n) + 1. - Robert Price, Oct 13 2013

Mathematica

Do[ If[ PrimeQ[(68*10^n - 41)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A000533, A002275, A101143.

Sequence in context: A243394 A175552 A279756 * A256247 A243595 A103807

Adjacent sequences: A103057 A103058 A103059 * A103061 A103062 A103063

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(19)-a(22) from Kamada data by Robert Price, Dec 14 2010

a(23) from Robert Price, Oct 13 2013

Status

approved