A104660 - OEIS

%I #23 Jan 25 2020 06:19:20

%S 1,1,2,2,1,3,3,1,2,2,1,2,2,3,3,3,3,3,4,3,3,6,3,4,3,3,6,4,1,5,1,4,3,5,

%T 3,6,4,2,6,2,2,3,5,3,4,4,4,2,2,4,4,3,4,5,6,3,3,5,2,4,3,5,4,4,3,6,4,3,

%U 6,6,4,5,4,2,4,5,2,4,5,6,4,4,3,6,5,4,5

%N Number of distinct prime divisors of 44...443 (with n 4s).

%H Amiram Eldar, <a href="/A104660/b104660.txt">Table of n, a(n) for n = 1..199</a>

%F a(n) = A001221(A173770(n+1)). - _Amiram Eldar_, Jan 25 2020

%e The number of distinct prime divisors of 43 is 1 (prime).

%e The number of distinct prime divisors of 443 is 1 (prime).

%e The number of distinct prime divisors of 4443 is 2.

%p A104660 := proc(n) x := [3,seq(4,k=1..n)] ; add(op(i,x)*10^(i-1),i=1..nops(x)) ; numtheory[factorset](%) ; nops(%) ; end proc:

%p seq(A104660(n),n=1..45) ; # _R. J. Mathar_, Aug 23 2011

%t Table[PrimeNu[FromDigits[Join[Table[4, {n}], {3}]]], {n, 50}] (* _Alonso del Arte_, Aug 23 2011 *)

%t Table[PrimeNu[FromDigits[PadLeft[{3},n,4]]],{n,2,70}] (* _Harvey P. Dale_, Aug 22 2016 *)

%Y Cf. A001221, A104518, A173770.

%K nonn,base

%O 1,3

%A _Parthasarathy Nambi_, Apr 21 2005

%E More terms from _R. J. Mathar_ and _Alonso del Arte_, Aug 23 2011

%E More terms from _Amiram Eldar_, Jan 25 2020