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 A306558 #7 Feb 24 2019 01:54:51
%S A306558 0,0,0,0,0,0,1,14,141,1267,10841,91091,764092
%N A306558 Number of double-crossing set partitions of {1,...,n}.
%C A306558 Two blocks of a set partitions double-cross each other if they are of the form {{...a...b...c...},{...x...y...z...}} for some a < x < b < y < c < z or x < a < y < b < z < c.
%H A306558 Kenneth J. Dykema, <a href="http://arxiv.org/abs/1602.03469">Generating functions for purely crossing partitions</a>, arXiv:1602.03469 [math.CO], 2016.
%e A306558 The a(7) = 14 double-crossing set partitions:
%e A306558 {{1,3,5},{2,4,6,7}}
%e A306558 {{1,3,6},{2,4,5,7}}
%e A306558 {{1,4,6},{2,3,5,7}}
%e A306558 {{1,2,4,6},{3,5,7}}
%e A306558 {{1,3,4,6},{2,5,7}}
%e A306558 {{1,3,5,6},{2,4,7}}
%e A306558 {{1,3,5,7},{2,4,6}}
%e A306558 {{1},{2,4,6},{3,5,7}}
%e A306558 {{1,3,5},{2,4,6},{7}}
%e A306558 {{1,3,5},{2,4,7},{6}}
%e A306558 {{1,3,6},{2,4,7},{5}}
%e A306558 {{1,3,6},{2,5,7},{4}}
%e A306558 {{1,4,6},{2},{3,5,7}}
%e A306558 {{1,4,6},{2,5,7},{3}}
%t A306558 croXXQ[stn_]:=MatchQ[stn,{___,{___,a_,___,b_,___,c_,___},___,{___,x_,___,y_,___,z_,___},___}/;a<x<b<y<c<z||x<a<y<b<z<c];
%t A306558 sps[{}]:={{}};sps[set:{i_,___}]:=Join@@Function[s,Prepend[#,s]&/@sps[Complement[set,s]]]/@Cases[Subsets[set],{i,___}];
%t A306558 Table[Length[Select[sps[Range[n]],croXXQ]],{n,0,8}]
%Y A306558 Cf. A000108, A000110, A001263, A002061, A005493, A007297, A016098 (crossing set partitions), A054726, A099947, A324166, A324172, A324324.
%K A306558 nonn,more
%O A306558 0,8
%A A306558 _Gus Wiseman_, Feb 23 2019