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 A342812 #15 Mar 23 2021 15:48:04
%S A342812 1,1,7,142,5895,417201,45046558,6891812712,1417730229765,
%T A342812 377158121463025
%N A342812 Volume of the (n-1)-dimensional associahedron in the Loday realization, multiplied by (n-1)!.
%C A342812 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.
%H A342812 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 10.3.
%t A342812 a[n_] := With[{npr = Subsets[Span @@ Range@n, {2}]}, Sum[With[{ip = Ordering@p}, Total[-p[[Table[Min@ip[[ij]], {ij, npr}]]]]^(n - 1)] / Times @@ Differences[p], {p, Permutations@Range@n}]];
%t A342812 Table[a[n], {n, 8}]
%Y A342812 Cf. A087422, A227414, A342811.
%K A342812 nonn,more
%O A342812 1,3
%A A342812 _Andrey Zabolotskiy_, Mar 22 2021