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A104239 Number of distinct prime factors of 135...(2n-1) (concatenation of n odd numbers). 0
0, 1, 2, 2, 2, 3, 2, 5, 3, 1, 4, 3, 3, 2, 3, 1, 5, 5, 7, 4, 5, 5, 4, 5, 5, 2, 4, 5, 4, 6, 5, 3, 7, 1, 4, 4, 3, 4, 3, 6, 5, 7, 5, 7, 8, 4, 7, 7, 1, 6 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Interestingly, 135791113151719 is prime.

LINKS

Table of n, a(n) for n=1..50.

Eric Weisstein's World of Mathematics, Consecutive Number sequences

EXAMPLE

The number of distinct prime factors of 13 is 1 (a prime) - the second term in the sequence.

The number of distinct prime factors of 135 is 2 - the third term in the sequence.

The number of distinct prime factors of 1357 is 2 - the fourth term in the sequence.

MATHEMATICA

Join[{0}, Table[PrimeNu[FromDigits[Flatten[IntegerDigits/@Range[1, 2n+1, 2]]]], {n, 50}]] (* Harvey P. Dale, Jun 15 2019 *)

CROSSREFS

Cf. A001221, A048847.

Sequence in context: A318058 A305434 A319478 * A283751 A132321 A058726

Adjacent sequences:  A104236 A104237 A104238 * A104240 A104241 A104242

KEYWORD

nonn,base

AUTHOR

Parthasarathy Nambi, Apr 16 2005

EXTENSIONS

Corrected and extended by Franklin T. Adams-Watters, Sep 01 2006

Edited by N. J. A. Sloane, May 21 2008 at the suggestion of R. J. Mathar

STATUS

approved

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Last modified October 14 08:54 EDT 2019. Contains 327995 sequences. (Running on oeis4.)