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 A073249 #14 Jun 17 2022 17:26:19
%S A073249 26,51,55,91,161,170,235,249,295,305,339,341,362,377,413,415,451,485,
%T A073249 489,530,551,559,579,595,629,638,649,651,665,667,685,687,703,721,723,
%U A073249 737,749,849,851,874,917,926,949,951,955,962,989,1015,1027,1057,1059
%N A073249 Nonprime squarefree numbers n such that both n-1 and n+1 are not squarefree and not prime.
%H A073249 Harvey P. Dale, <a href="/A073249/b073249.txt">Table of n, a(n) for n = 1..1000</a>
%t A073249 npsQ[n_]:=SquareFreeQ[n]&&NoneTrue[n+{1,0,-1},PrimeQ]&&NoneTrue[n+{1,-1},SquareFreeQ]; Select[Range[2000],npsQ] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jan 20 2019 *)
%t A073249 Mean/@SequencePosition[Table[Which[CompositeQ[n]&&SquareFreeQ[n],1,!SquareFreeQ[ n] && CompositeQ[ n],-1,True,0],{n,1100}],{-1,1,-1}] (* _Harvey P. Dale_, Jun 17 2022 *)
%Y A073249 Cf. A000469, A005117, A073247, A073250, A073251.
%K A073249 nonn
%O A073249 1,1
%A A073249 _Reinhard Zumkeller_, Jul 22 2002
%E A073249 Corrected by _Harvey P. Dale_, Jan 20 2019