OFFSET
2,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 2..1193
EXAMPLE
A135972(3) = 15 = 3*5 which has a(3)=2 distinct prime factors.
MATHEMATICA
k = {}; Do[If[ ! PrimeQ[2^n - 1], c = FactorInteger[2^n - 1]; d = Length[c]; AppendTo[k, d]], {n, 1, 100}]; k
CROSSREFS
KEYWORD
nonn
AUTHOR
Artur Jasinski, Dec 09 2007
EXTENSIONS
Offset set to 2, definition shortened - R. J. Mathar, Oct 01 2009
STATUS
approved