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A256721
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Numbers k such that R_k + 10 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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1
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1, 6, 10, 34, 36, 370, 8256, 13290, 14724, 427912, 685224
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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 + 89)/9 is prime.
Terms from Kamada data. Note Kamada does not recognize k=1 as 11 is a degenerate case of form AAA..ABA.
a(12) > 10^6.
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LINKS
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EXAMPLE
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For k=6, R_6 + 10 = 111111 + 10 = 111121 which is prime.
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MATHEMATICA
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Select[Range[0, 250000], PrimeQ[(10^# + 89)/9] &]
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PROG
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(Magma) [n: n in [1..400] | IsPrime((10^n+89) div 9)]; // Vincenzo Librandi, Apr 10 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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