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A165210
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Primes of the form (6^m - 1)/5.
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5
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OFFSET
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1,1
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COMMENTS
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Prime repunits in base 6 whose representation consists of m 1's. The exponents m are in A004062. a(5) and a(6) have 55 and 99 decimal digits, respectively.
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..9
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FORMULA
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a(n) = (6^A004062(n) - 1)/5.
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EXAMPLE
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a(2) = (6^A004062(2) - 1)/5 = (6^3 - 1)/5 = 215/5 = 43, which is 111_6.
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MATHEMATICA
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Select[Table[(6^n-1)/5, {n, 0, 2000}], PrimeQ] (* Vincenzo Librandi, Dec 09 2011 *)
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PROG
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(MAGMA) [a: n in [1..200] | IsPrime(a) where a is (6^n-1) div 5 ]; // Vincenzo Librandi, Dec 09 2011
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CROSSREFS
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Cf. A004062, A003464, A085104, A000668, A076481, A086122, A102170, A004022.
Sequence in context: A177507 A258182 A048605 * A162454 A203210 A323923
Adjacent sequences: A165207 A165208 A165209 * A165211 A165212 A165213
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KEYWORD
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nonn
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AUTHOR
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Rick L. Shepherd, Sep 07 2009
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STATUS
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approved
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