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%I #19 Apr 10 2020 01:42:49
%S 1,2,2,2,3,2,2,2,2,3,3,1,3,4,2,2,3,2,1,4,3,1,3,3,2,3,4,2,7,1,5,6,3,3,
%T 4,3,4,5,5,3,5,4,2,3,3,6,2,2,6,5,4,3,4,4,6,2,6,5,4,4,4,5,3,3,5,2,6,3,
%U 5,5,4,6,4,6,5,3,3,4,4,4,4,6,4,3,6,5,3
%N Number of distinct prime divisors of 77...771 (with n 7's).
%C Also number of distinct prime factors of (10^(n + 1) - 1)*7/9 - 6. - _Stefan Steinerberger_, Mar 01 2006
%H Amiram Eldar, <a href="/A104564/b104564.txt">Table of n, a(n) for n = 1..231</a>
%F a(n) = A001221(A173806(n+1)). - _Amiram Eldar_, Jan 24 2020
%e The number of distinct prime divisors of 71 is 1 (prime).
%e The number of distinct prime divisors of 771 is 2.
%e The number of distinct prime divisors of 7771 is 2.
%t Table[Length[FactorInteger[(10^(n + 1) - 1)*7/9 - 6]], {n, 1, 50}] (* _Stefan Steinerberger_, Mar 01 2006 *)
%t PrimeNu/@(FromDigits/@Table[PadLeft[{1},n,7],{n,2,55}]) (* _Harvey P. Dale_, Apr 22 2011 *)
%Y Cf. A001221, A104484, A104483, A173806.
%Y Cf. A104484 (3 instead of 7), A104659 (4 instead of 7), A104517 (5 instead of 7), A104890 (6 instead of 7), A105972 (8 instead of 7), A105259 (9 instead of 7).
%K nonn,base
%O 1,2
%A _Parthasarathy Nambi_, Apr 20 2005
%E More terms from _Stefan Steinerberger_, Mar 01 2006
%E Offset corrected and more terms added by _Amiram Eldar_, Jan 24 2020
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