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 A327437 #4 Sep 11 2019 20:22:51
%S A327437 1,1,3,6,15,52,410,32697
%N A327437 Number of unlabeled antichains of nonempty subsets of {1..n} that are either non-connected or non-covering (spanning edge-connectivity 0).
%C A327437 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 A327437 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 A327437 a(n > 0) = A306505(n) - A261006(n).
%e A327437 Non-isomorphic representatives of the a(1) = 1 through a(4) = 15 antichains:
%e A327437 {} {} {} {}
%e A327437 {{1}} {{1}} {{1}}
%e A327437 {{1},{2}} {{1,2}} {{1,2}}
%e A327437 {{1},{2}} {{1},{2}}
%e A327437 {{1},{2,3}} {{1,2,3}}
%e A327437 {{1},{2},{3}} {{1},{2,3}}
%e A327437 {{1,2},{1,3}}
%e A327437 {{1},{2},{3}}
%e A327437 {{1},{2,3,4}}
%e A327437 {{1,2},{3,4}}
%e A327437 {{1},{2},{3,4}}
%e A327437 {{1},{2},{3},{4}}
%e A327437 {{2},{1,3},{1,4}}
%e A327437 {{1,2},{1,3},{2,3}}
%e A327437 {{4},{1,2},{1,3},{2,3}}
%Y A327437 Column k = 0 of A327438.
%Y A327437 The labeled version is A327355.
%Y A327437 The covering case is A327426.
%Y A327437 Cf. A014466 A052446, A120338, A261005, A293606, A327201, A327236, A327352, A327353, A327354, A327438.
%K A327437 nonn,more
%O A327437 0,3
%A A327437 _Gus Wiseman_, Sep 11 2019