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A056717
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Numbers k such that 6*10^k + R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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1
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1, 5, 7, 25, 31, 112, 199, 533, 616, 718, 787, 1357, 2779, 3889, 4192, 7537, 7945, 23938, 32632, 49169, 56453, 61097, 90211
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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 (55*10^k - 1)/9 is prime.
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LINKS
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MATHEMATICA
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Do[ If[ PrimeQ[ 6*10^n + (10^n-1)/9], Print[n]], {n, 0, 10000}]
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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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56453 from Serge Batalov, Mar 12 2009 confirmed as next term by Ray Chandler, Feb 09 2012
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STATUS
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approved
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