A103027 Numbers n such that 6*10^n + R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

2, 3, 5, 11, 12, 23, 75, 101, 122, 173, 647, 2015, 2684, 11700, 19625

Offset

1,1

Comments

Also numbers n such that (55*10^n+17)/9 is prime.

a(16) > 10^5 - Robert Price, Sep 09 2015

Links

Table of n, a(n) for n=1..15.

Makoto Kamada, Prime numbers of the form 611...113.

Index entries for primes involving repunits.

Formula

a(n) = A101519(n) + 1.

Mathematica

Do[ If[ PrimeQ[(55*10^n + 17)/9], Print[n]], {n, 0, 10000}]
Select[Range[0, 10000], PrimeQ[(55 10^# + 17)/9] &] (* Vincenzo Librandi, Sep 10 2015 *)

Prog

(Magma) [n: n in [0..500]| IsPrime((55*10^n + 17) div 9)]; // Vincenzo Librandi, Sep 10 2015

Crossrefs

Cf. A002275, A101519.

Sequence in context: A243357 A066159 A316794 * A093902 A269004 A100475

Adjacent sequences: A103024 A103025 A103026 * A103028 A103029 A103030

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 18 2005

Extensions

Addition of a(14)-a(15) from Kamada data by Robert Price, Dec 12 2010

Status

approved