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%I #19 Dec 13 2022 07:55:42
%S 1,1,1,1,1,2,2,2,2,3,3,3,3,4,5,5,5,5,5,5,6,7,7,7,7,8,8,8,8,9,9,9,10,
%T 11,12,12,12,13,14,14,14,15,15,15,15,16,16,16,16,16,17,17,17,17,18,18,
%U 19,20,20,20,20,21,21,21,22,23,23,23,24,25,25,25,25,26
%N Number of squarefree numbers < n that are not prime.
%F a(n) = A013928(n+1) - A000720(n). [Corrected by _Georg Fischer_, Dec 13 2022]
%t Accumulate[Table[Boole[SquareFreeQ[n]&&!PrimeQ[n]],{n,1,100}]]
%Y Cf. A000720, A013928, A005117, A000040.
%K nonn
%O 1,6
%A _Enrique Pérez Herrero_, Mar 13 2012
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