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 A327808 #6 Oct 16 2019 13:10:36
%S A327808 0,0,1,3,9,32,233,16578
%N A327808 Number of unlabeled, disconnected, nonempty antichains of subsets of {1..n}.
%C A327808 An antichain is a set of nonempty sets, none of which is a subset of any other. A singleton is considered to be connected.
%F A327808 a(n) = A327424(n) - 1.
%e A327808 Non-isomorphic representatives of the a(2) = 1 through a(4) = 9 antichains:
%e A327808 {{1},{2}} {{1},{2}} {{1},{2}}
%e A327808 {{1},{2,3}} {{1},{2,3}}
%e A327808 {{1},{2},{3}} {{1},{2},{3}}
%e A327808 {{1},{2,3,4}}
%e A327808 {{1,2},{3,4}}
%e A327808 {{1},{2},{3,4}}
%e A327808 {{1},{2},{3},{4}}
%e A327808 {{2},{1,3},{1,4}}
%e A327808 {{4},{1,2},{1,3},{2,3}}
%Y A327808 The labeled version is A327354 - 1.
%Y A327808 The covering case is A327426.
%Y A327808 Unlabeled antichains that are either not connected or not covering are A327437.
%Y A327808 The version with empty antichains allowed is A327424.
%Y A327808 Cf. A000372, A014466, A120338, A293606, A326704, A327062, A327355.
%K A327808 nonn,more
%O A327808 0,4
%A A327808 _Gus Wiseman_, Sep 26 2019