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A095714
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Numbers k such that 9*R_k - 8 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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16
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3, 5, 7, 33, 45, 105, 197, 199, 281, 301, 317, 1107, 1657, 3395, 35925, 37597, 64305, 80139, 221631
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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 10^k - 9 is a prime.
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LINKS
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FORMULA
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EXAMPLE
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a(2) = 5, since 10^5 - 9 = 99991, which is prime.
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MATHEMATICA
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Do[ If[ PrimeQ[10^n - 9], Print[n]], {n, 0, 7000}]
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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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