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 A327355 #4 Sep 11 2019 20:22:08
%S A327355 1,1,4,14,83,1232,84625,109147467,38634257989625
%N A327355 Number of antichains of nonempty subsets of {1..n} that are either non-connected or non-covering (spanning edge-connectivity 0).
%C A327355 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.
%C A327355 The spanning edge-connectivity of a set-system is the minimum number of edges that must be removed (without removing incident vertices) to obtain a set-system that is disconnected or covers fewer vertices.
%F A327355 a(n) = A120338(n) + A014466(n) - A006126(n).
%e A327355 The a(1) = 1 through a(3) = 14 antichains:
%e A327355 {} {} {}
%e A327355 {{1}} {{1}}
%e A327355 {{2}} {{2}}
%e A327355 {{1},{2}} {{3}}
%e A327355 {{1,2}}
%e A327355 {{1,3}}
%e A327355 {{2,3}}
%e A327355 {{1},{2}}
%e A327355 {{1},{3}}
%e A327355 {{2},{3}}
%e A327355 {{1},{2,3}}
%e A327355 {{2},{1,3}}
%e A327355 {{3},{1,2}}
%e A327355 {{1},{2},{3}}
%Y A327355 Column k = 0 of A327352.
%Y A327355 The covering case is A120338.
%Y A327355 The unlabeled version is A327437.
%Y A327355 The non-spanning edge-connectivity version is A327354.
%Y A327355 Cf. A014466, A327071, A327148, A327353, A327426.
%K A327355 nonn,more
%O A327355 0,3
%A A327355 _Gus Wiseman_, Sep 10 2019