This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A104524 #23 Dec 03 2021 15:00:05
%S A104524 2,1,1,2,1,3,3,3,1,3,2,5,3,1,4,3,3,3,4,2,1,2,7,4,4,4,4,5,4,4,3,2,3,5,
%T A104524 3,4,3,7,2,4,2,4,4,8,2,4,3,6,3,2,4,7,7,7,5,5,6,7,2,4,6,3,5,5,2,5,2,4,
%U A104524 5,5,3,9,10,6,5,6,4,4,4,5,4,5,3,6,6,4,1
%N A104524 Number of distinct prime divisors of 55...557 (with n 5s).
%H A104524 Amiram Eldar, <a href="/A104524/b104524.txt">Table of n, a(n) for n = 1..192</a>
%F A104524 a(n) = A001221(A178769(n+1)). - _R. J. Mathar_, Aug 24 2011
%e A104524 The number of distinct prime divisors of 57 is 2.
%e A104524 The number of distinct prime divisors of 557 is 1 (prime).
%e A104524 The number of distinct prime divisors of 5557 is 1 (prime).
%p A104524 A104524 := proc(n) local x ;x := [7,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 A104524 Table[PrimeNu[(50*10^n + 13)/9], {n, 1, 50}](* _G. C. Greubel_, May 07 2017 *)
%t A104524 Table[PrimeNu[FromDigits[PadLeft[{7},n,5]]],{n,2,90}] (* _Harvey P. Dale_, Dec 03 2021 *)
%o A104524 (PARI) a(n) = omega((5*10^(n+1)+13)/9); \\ _Michel Marcus_, May 08 2017
%Y A104524 Cf. A104484, A104483, A104518.
%Y A104524 Cf. A001221, A178769.
%K A104524 nonn,base
%O A104524 1,1
%A A104524 _Parthasarathy Nambi_, Apr 20 2005
%E A104524 More terms from _Michel Marcus_, May 08 2017
%E A104524 More terms from _Amiram Eldar_, Jan 25 2020