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 A209628 #19 Dec 13 2022 07:55:42
%S A209628 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 A209628 11,12,12,12,13,14,14,14,15,15,15,15,16,16,16,16,16,17,17,17,17,18,18,
%U A209628 19,20,20,20,20,21,21,21,22,23,23,23,24,25,25,25,25,26
%N A209628 Number of squarefree numbers < n that are not prime.
%F A209628 a(n) = A013928(n+1) - A000720(n). [Corrected by _Georg Fischer_, Dec 13 2022]
%t A209628 Accumulate[Table[Boole[SquareFreeQ[n]&&!PrimeQ[n]],{n,1,100}]]
%Y A209628 Cf. A000720, A013928, A005117, A000040.
%K A209628 nonn
%O A209628 1,6
%A A209628 _Enrique Pérez Herrero_, Mar 13 2012