2,2

Table of n, a(n) for n=2..91.

a(n) = A001221(A135972(n)) .

A135972(3)=15=3*5 which has a(3)=2 distinct prime factors.

k = {}; Do[If[ ! PrimeQ[2^n - 1], c = FactorInteger[2^n - 1]; d = Length[c]; AppendTo[k, d]], {n, 1, 100}]; k

Cf. A046051, A046053, A022307, A135972.

Sequence in context: A181796 A319686 A067554 * A135615 A166469 A080226

Adjacent sequences: A135978 A135979 A135980 * A135982 A135983 A135984

nonn

Artur Jasinski, Dec 09 2007

Offset set to 2, definition shortened - R. J. Mathar, Oct 01 2009

approved