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A093938
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Primes of the form 2*10^k + 7*R_k, where R_k is the repunit (A002275) of length k.
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2
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2, 277, 2777, 2777777777, 2777777777777777, 2777777777777777777, 2777777777777777777777777777777777777, 2777777777777777777777777777777777777777777777777777777777777777
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..8.
Makoto Kamada, Prime numbers of the form 277...77.
Index entries for primes involving repunits
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MATHEMATICA
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Select[FromDigits/@Table[PadRight[{2}, n, 7], {n, 200}], PrimeQ] (* Harvey P. Dale, May 14 2011 *)
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CROSSREFS
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Cf. A002275, A056702 (corresponding k).
Sequence in context: A200168 A215043 A119553 * A172374 A231041 A080296
Adjacent sequences: A093935 A093936 A093937 * A093939 A093940 A093941
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KEYWORD
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nonn
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AUTHOR
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Rick L. Shepherd, Apr 17 2004
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STATUS
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approved
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