A259127 Numbers k such that 8*R_k + 3*10^k - 5 is prime, where R_k = 11...11 is the repunit (A002275) of length k.

2, 12, 30, 60, 116, 290, 632, 1064, 1494, 5432, 7362

Offset

1,1

Comments

Also, numbers k such that (35*10^k - 53)/9 is prime.

Terms from Kamada data.

a(12) > 10^5.

Links

Table of n, a(n) for n=1..11.

Makoto Kamada, Near-repdigit numbers of the form ABB...BBA.

Makoto Kamada, Prime numbers of the form 388...883.

Index entries for primes involving repunits.

Example

For k=2, 8*R_2 + 3*10^k - 5 = 88 + 300 - 5 = 383 which is prime.

Mathematica

Select[Range[100000], PrimeQ[(35*10^#-53)/9] &] (* adapted by Vincenzo Librandi, Jun 19 2015 *)

Crossrefs

Cf. A002275.

Sequence in context: A118239 A249055 A127118 * A296257 A301774 A286230

Adjacent sequences: A259124 A259125 A259126 * A259128 A259129 A259130

Keyword

more,hard,nonn

Author

Robert Price, Jun 18 2015

Extensions

Corrected Mathematica code from Vincenzo Librandi, Jun 19 2015

Status

approved