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 A304985 #10 Feb 23 2019 10:09:50
%S A304985 1,1,4,40,1344,203136,495598592,309065330371840,
%T A304985 14369391920653644779049472
%N A304985 Number of labeled clutters (connected antichains) spanning n vertices with singleton edges allowed.
%C A304985 Only the non-singleton edges are required to form an antichain.
%H A304985 Gus Wiseman, <a href="/A048143/a048143_4.txt">Sequences enumerating clutters, antichains, hypertrees, and hyperforests, organized by labeling, spanning, and allowance of singletons</a>.
%F A304985 For n > 1, a(n) = A048143(n) * 2^n.
%e A304985 The a(2) = 4 clutters:
%e A304985 {{1,2}}
%e A304985 {{1},{1,2}}
%e A304985 {{2},{1,2}}
%e A304985 {{1},{2},{1,2}}
%Y A304985 Cf. A048143, A198085, A261006, A304912, A304981, A304982, A304983, A304984, A304985, A304986.
%Y A304985 Cf. A000372, A006126, A014466, A304997, A304999, A306505, A317674, A319721.
%K A304985 nonn
%O A304985 0,3
%A A304985 _Gus Wiseman_, May 23 2018