%I #15 Nov 09 2021 06:41:36

%S 0,4,30,303,3053,30421,303857,3039127,30395383,303963673,3039652332,

%T 30396399068,303963519954,3039635209356,30396355530761,

%U 303963552535238,3039635510867921,30396355103617024,303963550950390745,3039635508820145344,30396355092470750098,303963550928711270447

%N Number of squarefree integers with an odd number of prime factors <= 10^n.

%C a(n) is the number of integers k <= 10^n with mu(k)=-1 where mu(k) is the Möbius function.

%F a(n) = (A071172(n) - A084237(n)) / 2.

%F Lim_{n->oo} a(n)/10^n = 3/Pi^2 (A104141).

%e a(1) = 4 because there are 4 squarefree integers with an odd number of prime factors <= 10: 2, 3, 5, 7.

%t Table[Length@Select[Range[10^n],MoebiusMu@#==-1&],{n,0,6}]

%Y Cf. A071172, A084237, A008683, A030059, A104141, A348709.

%K nonn

%O 0,2

%A _Giorgos Kalogeropoulos_, Oct 30 2021