A103073 Numbers n such that 8*10^n + R_n + 8 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 4, 7, 9, 19, 22, 70, 102, 121, 123, 235, 360, 594, 1614, 2410, 16048, 16174

Offset

1,2

Comments

Also numbers n such that (73*10^n+71)/9 is prime.

a(18) > 10^5. - Robert Price, Oct 13 2015

Links

Table of n, a(n) for n=1..17.

Makoto Kamada, Prime numbers of the form 811...119.

Index entries for primes involving repunits.

Formula

a(n) = A101060(n) + 1.

Mathematica

Do[ If[ PrimeQ[(73*10^n + 71)/9], Print[n]], {n, 0, 10000}]
Select[Range[0, 100000], PrimeQ[(73 10^# + 71)/9] &] (* Vincenzo Librandi, Oct 14 2015 *)

Prog

(Magma) [n: n in [0..400] | IsPrime((73*10^n+71) div 9)]; // Vincenzo Librandi, Oct 14 2015

Crossrefs

Cf. A002275, A101060.

Sequence in context: A044903 A359016 A281144 * A166742 A346554 A022541

Adjacent sequences: A103070 A103071 A103072 * A103074 A103075 A103076

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(16)-a(17) from Kamada data by Robert Price, Dec 14 2010

Status

approved