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A256570
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Numbers k such that 3*R_k + 10 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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0
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1, 2, 4, 5, 11, 16, 22, 24, 110, 232, 557, 566, 888, 1946, 2610, 3302, 10214, 41756, 89160, 120782
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OFFSET
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1,2
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COMMENTS
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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.
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LINKS
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EXAMPLE
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For k=4, 3*R_4 + 10 = 3333 + 10 = 3343 which is prime.
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MATHEMATICA
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Select[Range[0, 250000], PrimeQ[(10^# + 29)/3] &]
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PROG
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(Magma) [n: n in [0..400] | IsPrime((10^n+29) div 3)]; // Vincenzo Librandi, Apr 11 2015
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CROSSREFS
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KEYWORD
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more,hard,nonn
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AUTHOR
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STATUS
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approved
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