A102972 Numbers n such that 3*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 3, 6, 12, 33, 69, 111, 1965, 5646, 7404, 11103, 20790, 24840, 38199, 90669

Offset

1,3

Comments

Also numbers n such that (32*10^n+13)/9 is prime.

a(17) > 10^5. - Robert Price, Apr 07 2015

Links

Table of n, a(n) for n=1..16.

Makoto Kamada, Prime numbers of the form 355...557.

Index entries for primes involving repunits.

Formula

a(n) = A101837(n-1) + 1.

Mathematica

Do[ If[ PrimeQ[(32*10^n+13)/9], Print[n]], {n, 0, 10000}]
Select[Range[0, 10000], PrimeQ[(32 10^# + 13) / 9 ] &] (* Vincenzo Librandi, Apr 08 2015 *)

Prog

(Magma) [n: n in [0..200] | IsPrime((32*10^n+13) div 9)]; // Vincenzo Librandi, Apr 08 2015

Crossrefs

Cf. A002275, A101837.

Sequence in context: A026079 A066710 A033648 * A075209 A075207 A208131

Adjacent sequences: A102969 A102970 A102971 * A102973 A102974 A102975

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

Addition of a(12)-a(14) from Kamada data by Robert Price, Dec 13 2010

a(15) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

a(16) from Robert Price, Apr 07 2015

Status

approved