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A256570
Numbers k such that 3*R_k + 10 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
0
1, 2, 4, 5, 11, 16, 22, 24, 110, 232, 557, 566, 888, 1946, 2610, 3302, 10214, 41756, 89160, 120782
OFFSET
1,2
COMMENTS
Also, numbers k such that (10^k + 29)/3 is prime.
Terms from Kamada data. Note Kamada does not recognize k=1 as 13 is a degenerate case of form AAA..ABA.
a(21) > 2.5*10^5.
EXAMPLE
For k=4, 3*R_4 + 10 = 3333 + 10 = 3343 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(10^# + 29)/3] &]
PROG
(Magma) [n: n in [0..400] | IsPrime((10^n+29) div 3)]; // Vincenzo Librandi, Apr 11 2015
CROSSREFS
Cf. A002275.
Sequence in context: A294434 A191289 A370633 * A284427 A366702 A089416
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 10 2015
STATUS
approved