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A256760 Numbers k such that R_k + 60 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 0
1, 2, 4, 5, 8, 17, 19, 64, 368, 616, 857, 4351, 6526, 10555, 12685, 14549, 33886 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Also, numbers k such that (10^k + 539)/9 is prime.
Terms from Kamada data. Note that Kamada does not recognize k=1 as 61 is a degenerate case of form AAA..ABA.
a(18) > 2.5*10^5.
LINKS
EXAMPLE
For k=5, R_5 + 60 = 11111 + 60 = 11171 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(10^# + 539)/9] &]
PROG
(Magma) [n: n in [1..400] | IsPrime((10^n+539) div 9)]; // Vincenzo Librandi, Apr 10 2015
CROSSREFS
Cf. A002275.
Sequence in context: A045581 A253426 A092061 * A281646 A240460 A239405
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Apr 09 2015
STATUS
approved

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Last modified July 13 23:31 EDT 2024. Contains 374290 sequences. (Running on oeis4.)