A102968 Numbers n such that 3*10^n + 2*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

3, 5, 9, 12, 27, 51, 53, 147, 155, 257, 519, 603, 2885, 9509, 10524, 19650, 32508, 79445, 158909

Offset

1,1

Comments

Also numbers n such that (29*10^n+61)/9 is prime.

a(19) > 10^5. - Robert Price, Apr 05 2015

a(20) > 2*10^5. - Robert Price, Aug 12 2018

Links

Table of n, a(n) for n=1..19.

Makoto Kamada, Prime numbers of the form 322...229.

Index entries for primes involving repunits.

Formula

a(n) = A101831(n) + 1.

Mathematica

Do[ If[ PrimeQ[(29*10^n + 61)/9], Print[n]], {n, 0, 10000}]
Select[Range[10000], PrimeQ[(29 10^# + 61) / 9] &] (* Vincenzo Librandi, Apr 06 2015 *)

Prog

(Magma) [n: n in [0..500] | IsPrime((29*10^n + 61) div 9)]; // Vincenzo Librandi, Apr 06 2015

Crossrefs

Cf. A002275, A101831.

Sequence in context: A084593 A275843 A161866 * A180341 A348746 A177078

Adjacent sequences: A102965 A102966 A102967 * A102969 A102970 A102971

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

A(13) from Julien Peter Benney (jpbenney(AT)ftml.net), Jan 16 2005

A(14) from Robert G. Wilson v, Jan 17 2005

Addition of a(15)-a(16) from Kamada data by Robert Price, Dec 12 2010

a(17) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

a(18) from Robert Price, Apr 05 2015

a(19) from Robert Price, Aug 12 2018

Status

approved