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 A120338 #10 Sep 27 2019 08:45:01
%S A120338 0,1,4,30,546,41334,54502904,19317020441804
%N A120338 Number of disconnected antichain covers of a labeled n-set.
%C A120338 An antichain is a set of sets, none of which is a subset of any other. It is covering if there are no isolated vertices. - _Gus Wiseman_, Sep 26 2019
%e A120338 a(3)=4: the four disconnected covers are {{1},{2,3}}, {{2},{1,3}}, {{3},{1,2}} and {{1},{2},{3}}.
%t A120338 csm[s_]:=With[{c=Select[Subsets[Range[Length[s]],{2}],Length[Intersection@@s[[#]]]>0&]},If[c=={},s,csm[Sort[Append[Delete[s,List/@c[[1]]],Union@@s[[c[[1]]]]]]]]];
%t A120338 stableSets[u_,Q_]:=If[Length[u]==0,{{}},With[{w=First[u]},Join[stableSets[DeleteCases[u,w],Q],Prepend[#,w]&/@stableSets[DeleteCases[u,r_/;r==w||Q[r,w]||Q[w,r]],Q]]]];
%t A120338 Table[Length[Select[stableSets[Subsets[Range[n]],SubsetQ],Union@@#==Range[n]&&Length[csm[#]]!=1&]],{n,4}] (* _Gus Wiseman_, Sep 26 2019 *)
%Y A120338 Cf. A006126, A007153, A048143, A327355.
%Y A120338 Column k = 0 of A327351, if we assume a(0) = 1.
%Y A120338 Column k = 0 of A327357, if we assume a(0) = 1.
%Y A120338 The non-covering version is A327354.
%Y A120338 The unlabeled version is A327426.
%K A120338 nonn
%O A120338 1,3
%A A120338 _Greg Huber_, Jun 22 2006