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 A342811 #15 Mar 23 2021 15:45:04
%S A342811 1,13,1009,354161,496376001,2632501072321,52080136110870785,
%T A342811 3872046158193220660993,1099175272489026844687825921,
%U A342811 1210008580962784935280673680079873,5225407816779297641534116390319222362113
%N A342811 Volume of the permutohedron obtained from the coordinates 1, 2, 4, ..., 2^(n-1), multiplied by (n-1)!.
%C A342811 Here the volume is relative to the unit cell of the lattice which is the intersection of Z^n with the hyperplane spanning the polytope.
%C A342811 a(n) is the number of subgraphs of the complete bipartite graph K_{n-1,n} such that for any vertex from the 2nd part there is a matching that covers all other vertices; Postnikov calls the characterization of such subgraphs "the dragon marriage problem".
%H A342811 Alexander Postnikov, <a href="https://doi.org/10.1093/imrn/rnn153">Permutohedra, Associahedra, and Beyond</a>, International Mathematics Research Notices, 2009, 1026-1106; arXiv:<a href="https://arxiv.org/abs/math/0507163">math/0507163</a> [math.CO], 2005. See Example 5.5.
%t A342811 a[n_] := Sum[(p.(2^Range[0, n-1]))^(n-1) / Times @@ Differences[p], {p, Permutations@Range@n}];
%t A342811 Table[a[n], {n, 2, 8}]
%Y A342811 Cf. A066319 (analog for regular permutohedron), A087422, A227414, A342812.
%K A342811 nonn
%O A342811 2,2
%A A342811 _Andrey Zabolotskiy_, Mar 22 2021