A105972 - OEIS

%I #22 Apr 11 2020 22:01:26

%S 0,1,1,2,4,3,2,2,2,2,3,3,3,3,2,2,3,8,1,3,2,2,5,2,4,6,2,2,5,3,4,4,4,2,

%T 5,5,5,4,6,3,5,3,2,5,4,4,7,4,4,6,3,5,5,3,5,6,5,5,5,4,3,5,4,2,7,3,3,8,

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

%N Number of distinct prime divisors of 88...881 (with n 8's).

%H Amiram Eldar, <a href="/A105972/b105972.txt">Table of n, a(n) for n = 0..203</a>

%F a(n) = A001221(A173810(n+1)). - _Michel Marcus_, Jan 27 2014

%e The number of distinct prime divisors of 81 is 1.

%e The number of distinct prime divisors of 881 is 1 (prime).

%e The number of distinct prime divisors of 8881 is 2.

%t Table[PrimeNu[(8*10^(n+1) - 71)/9], {n,0,50}] (* _G. C. Greubel_, May 16 2017 *)

%t PrimeNu/@Table[10 FromDigits[PadRight[{},n,8]]+1,{n,0,90}] (* _Harvey P. Dale_, Apr 25 2019 *)

%o (PARI) a(n) = omega((8*10^(n+1)-71)/9); \\ _Michel Marcus_, Jan 27 2014

%Y Cf. A001221, A104564, A104517, A104659, A173810.

%K nonn,base

%O 0,4

%A _Parthasarathy Nambi_, Apr 28 2005

%E More terms from _Michel Marcus_, Jan 27 2014