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 A321406 #4 Nov 15 2018 08:40:50
%S A321406 1,0,0,0,0,0,1,1,1,2,4
%N A321406 Number of non-isomorphic self-dual set systems of weight n with no singletons.
%C A321406 Also the number of 0-1 symmetric matrices up to row and column permutations with sum of elements equal to n and no zero rows or columns, in which the rows are all different and none sums to 1.
%C A321406 The dual of a multiset partition has, for each vertex, one part consisting of the indices (or positions) of the parts containing that vertex, counted with multiplicity. For example, the dual of {{1,2},{2,2}} is {{1},{1,2,2}}.
%C A321406 The weight of a multiset partition is the sum of sizes of its parts. Weight is generally not the same as number of vertices.
%e A321406 Non-isomorphic representatives of the a(6) = 1 through a(10) = 4 set systems:
%e A321406 6: {{1,2},{1,3},{2,3}}
%e A321406 7: {{1,3},{2,3},{1,2,3}}
%e A321406 8: {{1,2},{1,3},{2,4},{3,4}}
%e A321406 9: {{1,2},{1,3},{1,4},{2,3,4}}
%e A321406 9: {{1,2},{1,4},{3,4},{2,3,4}}
%e A321406 10: {{1,2},{2,4},{1,3,4},{2,3,4}}
%e A321406 10: {{1,3},{2,4},{1,3,4},{2,3,4}}
%e A321406 10: {{1,4},{2,4},{3,4},{1,2,3,4}}
%e A321406 10: {{1,2},{1,3},{2,4},{3,5},{4,5}}
%Y A321406 Cf. A000219, A007716, A045778, A049311, A135588, A138178, A283877, A302545, A316980, A316983.
%Y A321406 Cf. A320796, A320797, A321401, A321402, A321403, A321405.
%K A321406 nonn,more
%O A321406 0,10
%A A321406 _Gus Wiseman_, Nov 15 2018