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 A124579 #4 Aug 18 2016 14:14:36
%S A124579 0,0,1,0,2,1,3,1,2,2,4,3,5,3,4,4,6,5,7,6,5,6,8,7,8,7,9,10,9,10,11,11,
%T A124579 8,9,10,12,12,11,12,13,13,14,15,14,15,13,16,16,17,18,14,19,17,20,15,
%U A124579 21,16,17,18,22,19,18,23,24,19,20,21,25,20,22,23,26,24,21,27,28,22,25,26,29
%N A124579 Number of natural numbers less than n which have identical Moebius mu values.
%e A124579 a(10) = 2 because in the first nine integers less than 10, mu(1) = mu(6) = mu(10).
%t A124579 a[n_] := a[n] = MoebiusMu@n; f[n_] := Count[a /@ Range[n - 1], a@n]; Array[f, 80]
%t A124579 With[{mu=MoebiusMu[Range[80]]},Table[Count[Take[mu,n],_?(#==MoebiusMu[ n+1]&)],{n,0,Length[mu]}]] (* _Harvey P. Dale_, Aug 18 2016 *)
%Y A124579 Cf. A124580.
%Y A124579 Cf. A008683, A002321.
%K A124579 nonn
%O A124579 1,5
%A A124579 _Robert G. Wilson v_, Nov 05 2006