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A135981 Number of distinct prime factors of A135972(n). 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

LINKS

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

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: A085082 A181796 A067554 * A135615 A166469 A080226

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

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Last modified February 17 16:15 EST 2018. Contains 299296 sequences. (Running on oeis4.)