A104518 - OEIS

%I #17 Jan 25 2020 08:01:01

%S 1,2,2,2,2,2,1,3,2,2,3,4,3,3,4,2,2,4,3,3,5,2,2,6,1,3,4,5,7,4,4,3,6,4,

%T 4,7,5,6,4,3,3,5,2,4,6,4,5,6,4,4,4,5,4,4,4,5,4,3,2,5,3,3,3,3,1,5,7,6,

%U 2,3,5,3,1,7,2,4,3,8,4,6,3,3,3,6,5,3,5

%N Number of distinct prime divisors of 55...3 (with n 5s).

%H Amiram Eldar, <a href="/A104518/b104518.txt">Table of n, a(n) for n = 1..199</a>

%F a(n) = A001221(A173802(n+1)). - _R. J. Mathar_, Aug 24 2011

%e The number of distinct prime divisors of 53 is 1 (prime) which is the first term in the sequence.

%e The number of distinct prime divisors of 553 is 2 which is the second term in the sequence.

%e The number of distinct prime divisors of 5553 is 2 which is the third term in the sequence.

%p A104518 := proc(n) local x ;x := [3,seq(5,k=1..n)] ; add(op(i,x)*10^(i-1),i=1..nops(x)) ; numtheory[factorset](%) ; nops(%) ; end proc: # _R. J. Mathar_, Aug 24 2011

%t Table[PrimeNu[(50*10^n - 23)/9], {n, 0, 50}] (* _G. C. Greubel_, May 06 2017 *)

%Y Cf. A001221, A173802.

%K nonn,base

%O 1,2

%A _Parthasarathy Nambi_, Apr 19 2005

%E More terms from _Amiram Eldar_, Jan 25 2020