A102971 Numbers n such that 3*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 6, 9, 15, 24, 48, 73, 75, 97, 249, 273, 2488, 14499, 74773, 87448

Offset

1,2

Comments

Also numbers n such that (32*10^n-41)/9 is prime.

a(16) > 10^5. - Robert Price, May 24 2015

Links

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

Makoto Kamada, Prime numbers of the form 355...551.

Index entries for primes involving repunits.

Formula

a(n) = A101835(n) + 1.

Mathematica

Do[ If[ PrimeQ[(32*10^n-41)/9], Print[n]], {n, 0, 10000}]
Select[Range[0, 10000], PrimeQ[(32 10^# - 41)/9] &] (* Vincenzo Librandi, May 25 2015 *)

Prog

(Magma) [n: n in [0..2000] | IsPrime((32*10^n-41) div 9)]; // Vincenzo Librandi, May 25 2015

Crossrefs

Cf. A002275, A101835.

Sequence in context: A097426 A075278 A316048 * A023885 A031209 A271826

Adjacent sequences: A102968 A102969 A102970 * A102972 A102973 A102974

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

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

a(14)-a(15) from Robert Price, May 24 2015

Status

approved