A135981 Number of distinct prime factors of A135972(n).

0, 2, 2, 3, 2, 3, 2, 4, 3, 3, 4, 4, 5, 3, 4, 2, 6, 3, 3, 3, 6, 3, 6, 5, 4, 3, 4, 8, 2, 3, 4, 7, 2, 6, 3, 7, 6, 4, 3, 9, 2, 7, 5, 7, 3, 6, 6, 8, 4, 6, 2, 11, 3, 6, 7, 3, 8, 2, 7, 4, 9, 3, 12, 3, 5, 7, 7, 4, 7, 3, 9, 6, 5, 2, 12, 3, 5, 6, 10, 11, 5, 9, 3, 6, 5, 12, 2, 5, 8, 12

Offset

2,2

Links

Amiram Eldar, Table of n, a(n) for n = 2..1193

Formula

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

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

Cf. A046051, A046053, A022307, A135972.

Sequence in context: A319686 A326082 A067554 * A135615 A348856 A166469

Adjacent sequences: A135978 A135979 A135980 * A135982 A135983 A135984

Keyword

nonn

Author

Artur Jasinski, Dec 09 2007

Extensions

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

Status

approved