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A056700
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Numbers k such that 2*10^k + R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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2
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0, 2, 3, 12, 18, 23, 57, 128, 543, 584, 833, 2450, 2810, 2873, 3671, 6384, 10296, 16704, 53049, 56544, 74253
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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 (19*10^k-1)/9 is prime.
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LINKS
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MATHEMATICA
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Do[ If[ PrimeQ[ 2*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,hard,more
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AUTHOR
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EXTENSIONS
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10296 and 16704 from Ray Chandler, Sep 2010
53049 and 56544 from Serge Batalov, Mar 2009 confirmed as next terms by Ray Chandler, Feb 03 2012
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STATUS
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approved
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