A104239 Number of distinct prime factors of 135...(2n-1) (concatenation of n odd numbers).

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

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: A305434 A319478 A341408 * 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