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A056705
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Numbers k such that 3*10^k + 7*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
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1
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OFFSET
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1,3
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COMMENTS
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Also numbers k such that (34*10^k - 7)/9 is prime.
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LINKS
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Table of n, a(n) for n=1..6.
Makoto Kamada, Prime numbers of the form 377...77.
Index entries for primes involving repunits
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MATHEMATICA
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Do[ If[ PrimeQ[ 3*10^n + 7*(10^n-1)/9], Print[n]], {n, 0, 30070}]
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CROSSREFS
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Cf. A002275, A093939.
Sequence in context: A228055 A132092 A226258 * A259744 A065706 A078874
Adjacent sequences: A056702 A056703 A056704 * A056706 A056707 A056708
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KEYWORD
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hard,nonn
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AUTHOR
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Robert G. Wilson v, Aug 10 2000
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STATUS
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approved
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