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 A355990 #17 Jul 22 2022 10:36:30
%S A355990 1,4,20,60,420,3360,10080,100800,1108800,3326400,43243200,605404800,
%T A355990 1816214400,29059430400,494010316800,1482030950400,28158588057600,
%U A355990 563171761152000,1689515283456000,37169336236032000,854894733428736000,2564684200286208000
%N A355990 a(n) = n! / (6 * floor(n/3)!).
%F A355990 E.g.f.: (1 - x^3) * (exp(x^3) - 1)/(6 * (1 - x)).
%F A355990 a(n) = A355988(n)/6.
%t A355990 a[n_] := n!/(6 * Floor[n/3]!); Array[a, 22, 3] (* _Amiram Eldar_, Jul 22 2022 *)
%o A355990 (PARI) a(n) = n!/(6*(n\3)!);
%o A355990 (PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace((1-x^3)*(exp(x^3)-1)/(6*(1-x))))
%Y A355990 Column 3 of A355996.
%Y A355990 Cf. A355988, A355989, A355991,
%K A355990 nonn,easy
%O A355990 3,2
%A A355990 _Seiichi Manyama_, Jul 22 2022