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A259128
Numbers k such that R_k + 3*10^k + 2 is prime, where R_k = 11...11 is the repunit (A002275) of length k.
0
0, 2, 12, 14, 30, 104, 126, 342, 600, 9824
OFFSET
1,2
COMMENTS
Also, numbers k such that (28*10^k + 17)/9 is prime.
Terms from Kamada data.
Note that Kamada does not recognize k=0 as 5 is a degenerate case of form ABB..BBA.
a(11) > 10^5.
EXAMPLE
For k=2, R_2 + 3*10^k + 2 = 11 300 + 2 = 313 which is prime.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(28*10^#+17)/9] &]
PROG
(Magma) [n: n in [0..400] | IsPrime((28*10^n+17) div 9)]; // Vincenzo Librandi, Jun 19 2015
CROSSREFS
Cf. A002275.
Sequence in context: A232768 A022368 A076484 * A280942 A270119 A340016
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jun 18 2015
STATUS
approved