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 A165210 Primes of the form (6^m - 1)/5. 5
 7, 43, 55987, 7369130657357778596659, 3546245297457217493590449191748546458005595187661976371 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..9 FORMULA a(n) = (6^A004062(n) - 1)/5. EXAMPLE a(2) = (6^A004062(2) - 1)/5 = (6^3 - 1)/5 = 215/5 = 43, which is 111_6. MATHEMATICA Select[Table[(6^n-1)/5, {n, 0, 2000}], PrimeQ] (* Vincenzo Librandi, Dec 09 2011 *) PROG (Magma) [a: n in [1..200] | IsPrime(a) where a is (6^n-1) div 5 ]; // Vincenzo Librandi, Dec 09 2011 CROSSREFS 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 KEYWORD nonn AUTHOR Rick L. Shepherd, Sep 07 2009 STATUS approved

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Last modified December 2 17:33 EST 2022. Contains 358510 sequences. (Running on oeis4.)