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 A266091 #28 Feb 21 2023 11:33:08
%S A266091 1,3,15,126,1782,42471,1706562,115640460,13216815036,2548124192970,
%T A266091 828751754742975,454739496669274500,420972227408592675000,
%U A266091 657522745057190417409000,1732789066323343611643088400,7704900186426840030325195822560,57807195523790513335568376591463776
%N A266091 a(n) = Product_{k=0..n} (3*k)!/(n+k)!.
%C A266091 a(n) gives the number of diagonally and antidiagonally symmetric alternating sign matrices (DASASM's) of order (2n+1) X (2n+1) (see Behrend et al. link).
%H A266091 Roger E. Behrend, Ilse Fischer, Matjaž Konvalinka, <a href="http://arxiv.org/abs/1512.06030">Diagonally and antidiagonally symmetric alternating sign matrices of odd order</a>, arXiv:1512.06030 [math.CO], 2015.
%F A266091 a(n) ~ Gamma(1/3)^(1/3) * exp(1/36) * n^(1/36) * 3^(3*n^2/2 + 2*n + 11/36) / (A^(1/3) * Pi^(1/6) * 2^(2*n^2 + 2*n + 7/12)), where A = A074962 is the Glaisher-Kinkelin constant. - _Vaclav Kotesovec_, Dec 21 2015
%F A266091 a(n) = Product_{1 <= i <= j <= n} (i + 2*j)/(i + j - 1). Note that Product_{1 <= i <= j <= n} (i + j)/(i + j - 1) = 2^n. - _Peter Bala_, Feb 19 2023
%t A266091 Table[Product[(3 k)!/(n + k)!, {k, 0, n}], {n, 0, 16}] (* _Vincenzo Librandi_, Dec 21 2015 *)
%o A266091 (PARI) a(n) = prod(k=0, n, (3*k)!/(n+k)!);
%o A266091 (Magma) [&*[Factorial(3*k)/Factorial(n+k): k in [0..n]]: n in [0..16]]; // _Vincenzo Librandi_, Dec 21 2015
%Y A266091 Cf. A005157, A086205.
%K A266091 nonn,easy
%O A266091 0,2
%A A266091 _Michel Marcus_, Dec 21 2015