The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A135981 Number of distinct prime factors of A135972(n). 1
 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 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 30 15:29 EDT 2021. Contains 346359 sequences. (Running on oeis4.)