A103057 Numbers n such that 7*10^n + 4*R_n - 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 4, 6, 7, 10, 16, 22, 31, 1315, 2064, 6150, 8707, 12252, 18610, 21630, 41712, 44808, 45421

Offset

1,2

Comments

Also numbers n such that (67*10^n-31)/9 is prime.

a(19) > 10^5. - Robert Price, Sep 28 2015

Links

Table of n, a(n) for n=1..18.

Makoto Kamada, Prime numbers of the form 744...441.

Index entries for primes involving repunits.

Formula

a(n) = A101139(n) + 1.

Mathematica

Do[ If[ PrimeQ[(67*10^n - 31)/9], Print[n]], {n, 0, 10000}]
Select[Range[10000], PrimeQ[(67 10^# - 31) / 9] &] (* Vincenzo Librandi, Sep 29 2015 *)

Prog

(Magma) [n: n in [0..500] | IsPrime((67*10^n-31) div 9)]; // Vincenzo Librandi, Sep 29 2015

Crossrefs

Cf. A002275, A101139.

Sequence in context: A310652 A310653 A310654 * A039590 A134038 A247546

Adjacent sequences: A103054 A103055 A103056 * A103058 A103059 A103060

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(13)-a(15) from Kamada data by Robert Price, Dec 14 2010

a(16)-a(18) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Status

approved