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A103021
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Numbers n such that 5*10^n + 7*R_n + 2 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, 3, 7, 15, 27, 129, 189, 333, 1324, 1600, 2199, 10000, 27751
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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 (52*10^n+11)/9 is prime.
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LINKS
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FORMULA
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EXAMPLE
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For n=0, (52*10^n+11)/9=7 which is prime, so 0 is in the sequence.
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MATHEMATICA
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Do[ If[ PrimeQ[(52*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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Addition of a(13) from Kamada data by Robert Price, Dec 13 2010
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STATUS
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approved
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