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 A304986 #10 May 23 2018 23:13:21
%S A304986 1,2,4,12,115,6834,7783198,2414627236078,56130437209370100252471
%N A304986 Number of labeled clutters (connected antichains) spanning some subset of {1,...,n}, if clutters of the form {{x}} are allowed for any vertex x.
%F A304986 a(n > 0) = A198085(n) + 1.
%F A304986 a(n) = A305005(n) + n.
%e A304986 The a(3) = 12 clutters:
%e A304986 {}
%e A304986 {{1}}
%e A304986 {{2}}
%e A304986 {{3}}
%e A304986 {{1,2}}
%e A304986 {{1,3}}
%e A304986 {{2,3}}
%e A304986 {{1,2,3}}
%e A304986 {{1,2},{1,3}}
%e A304986 {{1,2},{2,3}}
%e A304986 {{1,3},{2,3}}
%e A304986 {{1,2},{1,3},{2,3}}
%Y A304986 Cf. A048143, A198085, A261006, A304912, A304981, A304982, A304983, A304984, A304985, A304986.
%K A304986 nonn
%O A304986 0,2
%A A304986 _Gus Wiseman_, May 23 2018