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 A059489 #10 Jan 29 2019 10:07:20
%S A059489 1,5,66,2431,252586,74327145,62062015500,147198472495020,
%T A059489 992340657705109416,19023173201224270401428,
%U A059489 1037283901500845276138040124,160915151663568862349180293275135,71031251058324655345105192111798148156,89229337105909072018801794323387547092631236
%N A059489 Expansion of generating function A_{UU}^(2)(4n;1,1,1).
%H A059489 Paul Barry, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL19/Barry/barry321.html">Jacobsthal Decompositions of Pascal's Triangle, Ternary Trees, and Alternating Sign Matrices</a>, Journal of Integer Sequences, 19, 2016, #16.3.5.
%H A059489 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, but the formula is wrong]
%p A059489 A059489 := proc(n) local i, j, t1; t1 := (-3)^(n^2)*2^(2*n); for i to 2*n + 1 do for j to 2*n + 1 do if j mod 2 = 0 then t1 := t1*(3*j - 3*i + 2)/(j - i +2*n +1) end if end do end do; t1 end proc;
%K A059489 nonn,easy
%O A059489 0,2
%A A059489 _N. J. A. Sloane_, Feb 04 2001