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A102984
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Numbers n such that 4*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
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1
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0, 1, 2, 4, 7, 22, 23, 80, 4427, 31319, 80150, 91144
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OFFSET
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1,3
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COMMENTS
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Also numbers n such that (38*10^n-11)/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[(38*10^n - 11)/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(10) 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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