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 A215739 #13 Nov 20 2022 13:20:22
%S A215739 6,15,10,21,14,33,22,35,26,39,30,51,34,55,38,57,42,65,46,69,58,77,62,
%T A215739 85,66,87,70,91,74,93,78,95,82,105,86,111,94,115,102,119,106,123,110,
%U A215739 129,114,133,118,141,122,143,130,145,134,155,138,159,142,161,146,165
%N A215739 Even and odd composite squarefree numbers, interlaced.
%H A215739 Harvey P. Dale, <a href="/A215739/b215739.txt">Table of n, a(n) for n = 1..1000</a>
%F A215739 For k=1,2,.., a(2k-1)=A039956(k+1), a(2k)=A024556(k); A039956 Even squarefree numbers, A024556 Odd squarefree composite numbers.
%t A215739 Module[{nn=200,csfn,od,ev,len},csfn=Select[Range[nn],CompositeQ[ #] && SquareFreeQ[ #]&];od=Select[csfn,OddQ];ev=Select[csfn,EvenQ];len=Min[ Length[ od],Length[ev]];Riffle[Take[ev,len],Take[od,len]]] (* _Harvey P. Dale_, Nov 20 2022 *)
%Y A215739 Cf. A120944.
%K A215739 nonn
%O A215739 1,1
%A A215739 _Zak Seidov_, Aug 22 2012