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 A327426 #7 Sep 11 2019 20:22:35
%S A327426 1,1,1,2,6,23,201,16345
%N A327426 Number of non-connected, unlabeled, antichain covers of {1..n} (vertex-connectivity 0).
%C A327426 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. A singleton is not considered connected.
%C A327426 The vertex-connectivity of a set-system is the minimum number of vertices that must be removed (along with any resulting empty edges) to obtain a non-connected set-system or singleton. Note that this means a single node has vertex-connectivity 0.
%F A327426 a(n > 1) = A261005(n) - A261006(n).
%e A327426 Non-isomorphic representatives of the a(2) = 1 through a(5) = 23 antichains:
%e A327426 {1}{2} {1}{23} {1}{234} {1}{2345}
%e A327426 {1}{2}{3} {12}{34} {12}{345}
%e A327426 {1}{2}{34} {1}{2}{345}
%e A327426 {1}{24}{34} {1}{23}{45}
%e A327426 {1}{2}{3}{4} {12}{35}{45}
%e A327426 {1}{23}{24}{34} {1}{25}{345}
%e A327426 {1}{2}{3}{45}
%e A327426 {1}{245}{345}
%e A327426 {1}{2}{35}{45}
%e A327426 {1}{2}{3}{4}{5}
%e A327426 {1}{24}{35}{45}
%e A327426 {1}{25}{35}{45}
%e A327426 {12}{34}{35}{45}
%e A327426 {1}{24}{25}{345}
%e A327426 {1}{23}{245}{345}
%e A327426 {1}{2}{34}{35}{45}
%e A327426 {1}{235}{245}{345}
%e A327426 {1}{23}{24}{35}{45}
%e A327426 {1}{25}{34}{35}{45}
%e A327426 {1}{23}{24}{25}{345}
%e A327426 {1}{234}{235}{245}{345}
%e A327426 {1}{24}{25}{34}{35}{45}
%e A327426 {1}{23}{24}{25}{34}{35}{45}
%Y A327426 Column k = 0 of A327359.
%Y A327426 The labeled version is A120338.
%Y A327426 The non-covering version is A327424 (partial sums).
%Y A327426 Cf. A014466, A261005, A327354, A327355, A327437.
%K A327426 nonn,more
%O A327426 0,4
%A A327426 _Gus Wiseman_, Sep 11 2019