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 A304984 #7 May 23 2018 23:13:08
%S A304984 1,2,7,56,1533,210302,496838435,309068803876372,
%T A304984 14369391923126181310256825
%N A304984 Number of labeled clutters (connected antichains) spanning some subset of {1,...,n} with singleton edges allowed.
%F A304984 Binomial transform of A304985(n > 0).
%e A304984 The a(2) = 7 clutters:
%e A304984 {}
%e A304984 {{1}}
%e A304984 {{2}}
%e A304984 {{1,2}}
%e A304984 {{1},{1,2}}
%e A304984 {{2},{1,2}}
%e A304984 {{1},{2},{1,2}}
%Y A304984 Cf. A048143, A198085, A261006, A304912, A304981, A304982, A304983, A304984, A304985, A304986.
%K A304984 nonn
%O A304984 0,2
%A A304984 _Gus Wiseman_, May 23 2018