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A256606
Numbers k such that 3*R_k + 40 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
0
1, 2, 3, 4, 7, 8, 33, 38, 157, 252, 359, 365, 567, 876, 3108, 5780, 12987, 14984, 22287, 31574, 37473, 40984, 49806, 51364, 62451
OFFSET
1,2
COMMENTS
Also, numbers k such that (10^k + 119)/3 is prime.
Terms from Kamada data. Note Kamada does not recognize k=1 as 43 is a degenerate case of form AAA..ABA.
a(26) > 3*10^5.
EXAMPLE
For k=3, 3*R_3 + 40 = 333 + 40 = 373 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(10^# + 119)/3] &]
PROG
(PARI) is(n)=ispseudoprime(10^n\3+40) \\ Charles R Greathouse IV, Apr 10 2015
(Magma) [n: n in [0..400] | IsPrime((10^n+119) div 3)]; // Vincenzo Librandi, Apr 11 2015
CROSSREFS
Cf. A002275.
Sequence in context: A134459 A225211 A159554 * A101128 A182802 A172024
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 10 2015
STATUS
approved