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A102978
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Numbers n such that 3*10^n + 8*R_n - 7 is a prime, where R_n = 11...1 is the repunit (A002275) of length n.
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2
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1, 3, 19, 30, 40, 42, 45, 70, 307, 538, 1609, 1668, 1674, 4492, 4935, 6112, 12819, 14079, 16020, 23005, 50997, 82870
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OFFSET
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1,2
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COMMENTS
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Also numbers n such that (35*10^n-71)/9 is a prime.
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LINKS
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FORMULA
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MATHEMATICA
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Do[ If[ PrimeQ[(35*10^n - 71)/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(17)-a(20) from Kamada data by Robert Price, Dec 10 2010
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STATUS
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approved
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