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 A059491 #10 Sep 11 2017 02:36:49
%S A059491 1,1,6,189,30618,25332021,106698472452,2283997201168644,
%T A059491 248218139523497121576,136861610819571430116630660,
%U A059491 382684747771430768732371981946100,5424628155237728987530088501811168904125,389729317367139375014273384868937660572301897500
%N A059491 Expansion of generating function A_{QT}^(1)(4n;3).
%H A059491 G. C. Greubel, <a href="/A059491/b059491.txt">Table of n, a(n) for n = 0..50</a>
%H A059491 G. Kuperberg, <a href="https://arxiv.org/abs/math/0008184">Symmetry classes of alternating-sign matrices under one roof</a>, arXiv:math/0008184 [math.CO], 2000-2001 [Th. 5].
%F A059491 a(n) = 3^(n*(n-1)/2)*A005130(n).
%F A059491 a(n+1) is the Hankel transform of A097188. Odd terms occur in a(n+1) at positions given by 2*A000975(n). - _Paul Barry_, Feb 09 2007
%t A059491 f[n_] := Product[(3 k + 1)!/(n + k)!, {k, 0, n - 1}]; Table[3^(n*(n - 1)/2)*f[n], {n,0,20}] (* _G. C. Greubel_, Sep 10 2017 *)
%K A059491 nonn,easy
%O A059491 0,3
%A A059491 _N. J. A. Sloane_, Feb 04 2001