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 A320768 #28 Dec 01 2024 10:05:34
%S A320768 1,1,2,15,2420,333947200
%N A320768 Number of set partitions of the set of nonempty subsets of {1,...,n} where each block's elements are pairwise disjoint sets.
%e A320768 The a(3) = 15 set partitions:
%e A320768 {{{1}},{{2}},{{3}},{{1,2}},{{1,3}},{{2,3}},{{1,2,3}}}
%e A320768 {{{1}},{{2}},{{3},{1,2}},{{1,3}},{{2,3}},{{1,2,3}}}
%e A320768 {{{1}},{{2},{3}},{{1,2}},{{1,3}},{{2,3}},{{1,2,3}}}
%e A320768 {{{1}},{{2},{1,3}},{{3}},{{1,2}},{{2,3}},{{1,2,3}}}
%e A320768 {{{1}},{{2},{1,3}},{{3},{1,2}},{{2,3}},{{1,2,3}}}
%e A320768 {{{1},{2}},{{3}},{{1,2}},{{1,3}},{{2,3}},{{1,2,3}}}
%e A320768 {{{1},{2}},{{3},{1,2}},{{1,3}},{{2,3}},{{1,2,3}}}
%e A320768 {{{1},{3}},{{2}},{{1,2}},{{1,3}},{{2,3}},{{1,2,3}}}
%e A320768 {{{1},{3}},{{2},{1,3}},{{1,2}},{{2,3}},{{1,2,3}}}
%e A320768 {{{1},{2,3}},{{2}},{{3}},{{1,2}},{{1,3}},{{1,2,3}}}
%e A320768 {{{1},{2,3}},{{2}},{{3},{1,2}},{{1,3}},{{1,2,3}}}
%e A320768 {{{1},{2,3}},{{2},{3}},{{1,2}},{{1,3}},{{1,2,3}}}
%e A320768 {{{1},{2,3}},{{2},{1,3}},{{3}},{{1,2}},{{1,2,3}}}
%e A320768 {{{1},{2,3}},{{2},{1,3}},{{3},{1,2}},{{1,2,3}}}
%e A320768 {{{1},{2},{3}},{{1,2}},{{1,3}},{{2,3}},{{1,2,3}}}
%t A320768 spsu[_,{}]:={{}};spsu[foo_,set:{i_,___}]:=Join@@Function[s,Prepend[#,s]&/@spsu[Select[foo,Complement[#,Complement[set,s]]=={}&],Complement[set,s]]]/@Cases[foo,{i,___}];
%t A320768 sps[set_]:=spsu[Rest[Subsets[set]],set];
%t A320768 Table[Length[spsu[Sort/@Union@@sps/@Rest[Subsets[Range[n]]],Rest[Subsets[Range[n]]]]],{n,4}]
%Y A320768 Cf. A000110, A000258, A008277, A318391, A318392, A318393, A318394, A319884.
%K A320768 nonn,more
%O A320768 0,3
%A A320768 _Gus Wiseman_, Dec 09 2018
%E A320768 a(5) from, and definition clarified by _Christian Sievers_, Nov 30 2024