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a(n) is the number of squarefree composite numbers < prime(n).
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%I #8 Aug 12 2020 03:18:57

%S 0,0,0,1,2,2,4,4,6,7,8,11,13,14,15,16,19,19,22,24,24,27,28,31,35,35,

%T 36,38,38,40,46,48,50,51,56,56,58,61,63,64,67,67,73,73,75,75,82,90,91,

%U 91,93,96,96,99,102,105,108,108,110,111,112,117,124,126,126,127

%N a(n) is the number of squarefree composite numbers < prime(n).

%H Hugo Pfoertner, <a href="/A337030/b337030.txt">Table of n, a(n) for n = 1..10000</a>

%F a(1) = 0; a(n+1) = a(n) + A061398(n-1) for n>1.

%e a(1) = a(2) = a(3) = 0 because the only composite number < 5 is the square 4.

%e a(4) = 1: 6 is the first squarefree composite number < prime(4) = 7.

%o (PARI) m=0;pp=0;forprime(p=2,320,forcomposite(c=pp,p,if(issquarefree(c),m++));print1(m,", ");pp=p)

%Y Cf. A061398, A120944.

%K nonn

%O 1,5

%A _Hugo Pfoertner_, Aug 11 2020