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Number of squarefree numbers < n that are not prime.
0

%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 PĂ©rez Herrero_, Mar 13 2012