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
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Sep 07 2009
STATUS
approved