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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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1, 3, 7, 15, 27, 129, 189, 333, 1324, 1600, 2199, 10000, 27751
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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 (52*10^n+11)/9 is prime.
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LINKS
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Table of n, a(n) for n=1..13.
Makoto Kamada, Factorizations of 577...779.
Index entries for primes involving repunits.
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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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Sequence in context: A143701 A147638 A147394 * A025587 A101498 A027965
Adjacent sequences: A103018 A103019 A103020 * A103022 A103023 A103024
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KEYWORD
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more,nonn
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AUTHOR
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Robert G. Wilson v, Jan 18 2005
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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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