A104889 - OEIS

%I #11 Jan 27 2020 08:26:39

%S 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,

%T 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,

%U 2,4,7,7,3,5,3,3,3,5,4,10,5,4,3,5,3,2,4

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

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

%H Amiram Eldar, <a href="/A104889/b104889.txt">Table of n, a(n) for n = 1..201</a>

%F a(n) = A001221(A173772(n+1)). - _Amiram Eldar_, Jan 27 2020

%e Number of distinct prime divisors of 47 is 1 (prime).

%e Number of distinct prime divisors of 447 is 2.

%e Number of distinct prime divisors of 4447 is 1 (prime).

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

%Y Cf. A001221, A104564, A173772.

%K nonn

%O 1,2

%A _Parthasarathy Nambi_, Apr 24 2005

%E More terms from _Stefan Steinerberger_, Feb 21 2006

%E Offset corrected and more terms added by _Amiram Eldar_, Jan 27 2020