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 A019448 #43 Jan 08 2025 11:57:33
%S A019448 1,1,2,5,16,58,231,1016,4782,23653,121727,648611,3541871,19713695
%N A019448 Number of monomials in expansion of determinant of an n X n Hankel matrix [ t(i+j) ] in terms of its entries.
%H A019448 Benjamin Basso and Lance J. Dixon, <a href="https://arxiv.org/abs/1705.03545">Gluing Ladders into Fishnets</a>, arXiv:1705.03545 [hep-th], 2017. See p. 5.
%p A019448 with(linalg): A019448 := proc(n) local i, j, m; m := array(1..n, 1..n); for i from 1 to n do for j from 1 to n do m[i, j] := a[i+j] od od; nops([coeffs(det(m))]); end; # _Jeffrey Shallit_, Jun 08 2000
%p A019448 with(LinearAlgebra): f:=n->nops([coeffs(Determinant(Matrix(n, (i, j) -> a[i+j] )))]): [seq(f(n), n=0..10)]; # _Vaclav Kotesovec_, Mar 29 2019
%t A019448 f[n_] := Length@ Expand@ Det@ Table[t[i + j], {i, n}, {j, n}]; Do[ Print@ f@n, {n, 11}] (* _Robert G. Wilson v_, Sep 17 2006 *)
%Y A019448 Cf. A019447, A019589, A086647.
%K A019448 nonn,hard,more
%O A019448 0,3
%A A019448 Herbert S. Wilf
%E A019448 a(8)-a(9) from _Jeffrey Shallit_, Jun 08 2000
%E A019448 a(10)-a(11) from _Robert G. Wilson v_, Sep 17 2006
%E A019448 a(12) from _Roman Pearce_, Aug 30 2014
%E A019448 a(13) from _Vaclav Kotesovec_, Mar 20 2019
%E A019448 a(0)=1 prepended by _Alois P. Heinz_, Jan 08 2025