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A056663
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Numbers k such that 80*R_k + 9 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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2
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1, 13, 16, 34, 4174, 4471, 9811, 12259, 12340, 13759, 14575, 53410, 144682, 148327
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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 (8*10^(k+1) + 1)/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[ 80*(10^n - 1)/9 + 9 ], Print[n]], {n, 0, 30000}]
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CROSSREFS
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KEYWORD
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hard,nonn
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AUTHOR
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EXTENSIONS
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Intermediate missing terms 9811 (from M. Kamada), 12259, 12340, 13759 added by Serge Batalov, Dec 14 2008
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STATUS
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approved
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