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 A064633 #21 Sep 27 2022 09:22:56
%S A064633 1,9,216,9720,699840,73483200,10581580800,1999918771200,
%T A064633 479980505088000,142554210011136000,51319515604008960000,
%U A064633 22016072194119843840000,11096100385836401295360000,6491218725714294757785600000,4362098983680006077231923200000
%N A064633 a(n) = 3^n*n!*(n+2)!/2!.
%H A064633 Harry J. Smith, <a href="/A064633/b064633.txt">Table of n, a(n) for n = 0..75</a>
%F A064633 Hypergeometric g.f.: (1-3*x)^(-3).
%F A064633 a(0)=1, a(n) = n!*subs(x=0, (d^n/dx^n)(-1/((3*x-1)^3))), n = 1, 2, ...
%F A064633 From _Amiram Eldar_, Sep 27 2022: (Start)
%F A064633 Sum_{n>=0} 1/a(n) = 6*BesselI(2,2/sqrt(3)).
%F A064633 Sum_{n>=0} (-1)^n/a(n) = 6*BesselJ(2,2/sqrt(3)). (End)
%t A064633 Table[3^n n! (n+2)!/2,{n,0,20}] (* _Harvey P. Dale_, Feb 25 2015 *)
%o A064633 (PARI) { for (n=0, 75, write("b064633.txt", n, " ", 3^n*n!*(n + 2)!/2) ) } \\ _Harry J. Smith_, Sep 20 2009
%Y A064633 Cf. A000244, A010791.
%K A064633 nonn
%O A064633 0,2
%A A064633 _Karol A. Penson_, Oct 01 2001