A103061 Numbers n such that 7*10^n + 5*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 4, 18, 19, 646, 814, 5794, 16524, 19495, 26010, 29238, 72120

Offset

1,3

Comments

Also numbers n such that (68*10^n-23)/9 is prime.

a(14) > 10^5. - Robert Price, Oct 01 2015

Links

Table of n, a(n) for n=1..13.

Makoto Kamada, Prime numbers of the form 755...553.

Index entries for primes involving repunits.

Formula

a(n) = A101144(n-1) + 1 for n>1.

Mathematica

Do[ If[ PrimeQ[(68*10^n - 23)/9], Print[n]], {n, 0, 10000}]
Select[Range[10000], PrimeQ[(68 10^# - 23)/9] &] (* Vincenzo Librandi, Oct 02 2015 *)

Prog

(Magma) [n: n in [0..100]| IsPrime((68*10^n-23) div 9)]; // Vincenzo Librandi, Oct 02 2015
(PARI) for(n=0, 1e4, if (isprime((68*10^n-23)/9), print1(n", "))) \\ Altug Alkan, Oct 02 2015

Crossrefs

Cf. A002275, A101144.

Sequence in context: A081420 A039277 A045019 * A230605 A201880 A022384

Adjacent sequences: A103058 A103059 A103060 * A103062 A103063 A103064

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(9)-a(12) from Kamada data by Robert Price, Dec 14 2010

a(1)=0 inserted and a(13) added by Robert Price, Oct 01 2015

Status

approved