A105248 - OEIS

%I #21 Jan 14 2024 13:28:19

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

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

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

%N Number of distinct prime divisors of 88...887 (with n 8's).

%H Amiram Eldar, <a href="/A105248/b105248.txt">Table of n, a(n) for n = 0..199</a>

%F a(n) = A001221(A173812(n+1)). - _Michel Marcus_, Jan 27 2014

%e The number of distinct prime divisors of 87 is 2.

%e The number of distinct prime divisors of 887 is 1 (prime).

%e The number of distinct prime divisors of 8887 is 1 (prime).

%t Table[PrimeNu[(8*10^(n + 1) - 17)/9], {n, 1, 50}] (* _G. C. Greubel_, May 21 2017 *)

%o (PARI) a(n) = omega((8*10^(n+1)-17)/9); \\ _Michel Marcus_, Jan 27 2014

%Y Cf. A104524, A104889.

%K nonn,base

%O 0,2

%A _Parthasarathy Nambi_, Apr 29 2005

%E More terms from Brian Lauer (bel136(AT)psu.edu), Feb 23 2006

%E Corrected and extended by _Michel Marcus_, Jan 27 2014

%E More terms from _Amiram Eldar_, Jan 27 2020