A104889 Number of distinct prime divisors of 44...447 (with n 4s).

1, 2, 1, 2, 3, 2, 2, 4, 1, 3, 2, 3, 2, 2, 2, 2, 3, 3, 1, 5, 4, 4, 4, 7, 1, 4, 2, 5, 3, 3, 3, 3, 3, 6, 4, 5, 3, 2, 3, 5, 6, 7, 4, 4, 4, 2, 5, 3, 3, 6, 4, 6, 2, 5, 3, 5, 3, 6, 4, 6, 4, 6, 3, 5, 6, 6, 4, 5, 2, 4, 7, 7, 3, 5, 3, 3, 3, 5, 4, 10, 5, 4, 3, 5, 3, 2, 4

Offset

1,2

Comments

Also number of distinct prime factors of (10^(n + 1) - 1)*4/9 + 3. - Stefan Steinerberger, Feb 21 2006

Links

Amiram Eldar, Table of n, a(n) for n = 1..201

Formula

a(n) = A001221(A173772(n+1)). - Amiram Eldar, Jan 27 2020

Example

Number of distinct prime divisors of 47 is 1 (prime).
Number of distinct prime divisors of 447 is 2.
Number of distinct prime divisors of 4447 is 1 (prime).

Mathematica

Table[Length[FactorInteger[(10^(n + 1) - 1)*4/9 + 3]], {n, 1, 40}] (* Stefan Steinerberger, Feb 21 2006 *)

Crossrefs

Cf. A001221, A104564, A173772.

Sequence in context: A365543 A058071 A174961 * A356122 A290979 A117910

Adjacent sequences: A104886 A104887 A104888 * A104890 A104891 A104892

Keyword

nonn

Author

Parthasarathy Nambi, Apr 24 2005

Extensions

More terms from Stefan Steinerberger, Feb 21 2006

Offset corrected and more terms added by Amiram Eldar, Jan 27 2020

Status

approved