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A099409
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Numbers k such that 2*R_k + 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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3
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OFFSET
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1,3
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COMMENTS
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Also numbers k such that (2*10^k + 43)/9 is prime.
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LINKS
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FORMULA
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MATHEMATICA
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Do[ If[ PrimeQ[ 2(10^n - 1)/9 + 5], Print[n]], {n, 0, 5000}]
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PROG
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(Magma) [n: n in [0..1000] | IsPrime( 2*(10^n - 1) div 9 + 5)]; // Vincenzo Librandi, Oct 28 2014
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CROSSREFS
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KEYWORD
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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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