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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.
0
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.
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 A375623 A301774
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Jun 18 2015
EXTENSIONS
Corrected Mathematica code from Vincenzo Librandi, Jun 19 2015
STATUS
approved