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A102931
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Numbers k such that 10^k + 2*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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2
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1, 3, 6, 51, 57, 63, 150, 393, 420, 547, 42024, 43063, 101613, 107385
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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 (11*10^k + 61)/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[(11*10^n + 61)/9], Print[n]], {n, 0, 10000}]
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CROSSREFS
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KEYWORD
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more,nonn
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AUTHOR
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EXTENSIONS
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a(11)-a(12) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
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STATUS
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approved
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