login
A104889
Number of distinct prime divisors of 44...447 (with n 4s).
3
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
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
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