2,1

F(n)-1 is even if n is not a multiple of 3.

Chai Wah Wu, Table of n, a(n) for n = 2..379

a(n) = A020639(A000071(3n)).

Table[FactorInteger[Fibonacci[3n]-1][[1, 1]], {n, 2, 80}] (* Harvey P. Dale, Aug 08 2017 *)

(PARI) A138859(n)=factor(fibonacci(3*n)-1)[1, 1] /* A138859 is defined only for n>1 ! */

Cf. A000071.

Sequence in context: A084000 A168197 A257324 * A257328 A076569 A061194

Adjacent sequences: A138856 A138857 A138858 * A138860 A138861 A138862

nonn

M. F. Hasler, Apr 05 2008

approved