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A259127
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Numbers k such that 8*R_k + 3*10^k - 5 is prime, where R_k = 11...11 is the repunit (A002275) of length k.
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0
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2, 12, 30, 60, 116, 290, 632, 1064, 1494, 5432, 7362
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OFFSET
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1,1
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COMMENTS
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Also, numbers k such that (35*10^k - 53)/9 is prime.
Terms from Kamada data.
a(12) > 10^5.
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LINKS
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EXAMPLE
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For k=2, 8*R_2 + 3*10^k - 5 = 88 + 300 - 5 = 383 which is prime.
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MATHEMATICA
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Select[Range[100000], PrimeQ[(35*10^#-53)/9] &] (* adapted by Vincenzo Librandi, Jun 19 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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EXTENSIONS
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STATUS
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approved
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