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 A306642 #22 Dec 02 2021 13:31:26
%S A306642 1,12,900,94080,11988900,1704214512,260453217024,41886697881600,
%T A306642 6996546610936740,1203384096358158000,211855235800656848400,
%U A306642 38011289046678107596800,6928290032159649797280000,1279703438754969901486464000,239070018975087493229806080000
%N A306642 a(n) = Sum_{k=0..n} (3*n)!/(k! * (n-k)!)^3.
%H A306642 Seiichi Manyama, <a href="/A306642/b306642.txt">Table of n, a(n) for n = 0..431</a>
%H A306642 Robert W. Donley Jr, <a href="https://arxiv.org/abs/2107.09463">Directed path enumeration for semi-magic squares of size three</a>, arXiv:2107.09463 [math.CO], 2021.
%F A306642 a(n) ~ 216^n / (Pi*n)^2. - _Vaclav Kotesovec_, Jun 21 2021
%t A306642 Array[Sum[(3 #)!/(k!*(# - k)!)^3, {k, 0, #}] &, 15, 0] (* _Michael De Vlieger_, Dec 02 2021 *)
%o A306642 (PARI) {a(n) = sum(k=0, n, (3*n)!/(k!*(n-k)!)^3)}
%Y A306642 Column 3 of A306641.
%K A306642 nonn
%O A306642 0,2
%A A306642 _Seiichi Manyama_, Mar 02 2019