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 A064335 #20 Apr 25 2025 14:39:22
%S A064335 3,4,36,864,40320,3110400,359251200,58118860800,12553673932800,
%T A064335 3492203839488000,1216451004088320000,518769566666588160000,
%U A064335 265906457885674045440000,161316584450642254233600000
%N A064335 a(n) = 6*(2*n)!/(n+2).
%C A064335 All terms, except a(0) and a(1), are integer multiples of 6.
%H A064335 Harry J. Smith, <a href="/A064335/b064335.txt">Table of n, a(n) for n = 0..100</a>
%F A064335 a(n) = Integral_{x=0..oo} (x^n*(exp(-sqrt(x)) * (-1+sqrt(x)+2/sqrt(x)) + x*Ei(-sqrt(x))) ), n=0, 1..., where Ei(y) is the exponential integral. Representation as the n-th moment of a positive function on a positive half-axis, in Maple notation. This representation is unique.
%t A064335 Table[6*(2*n)!/(n+2), {n,0,20}] (* _G. C. Greubel_, May 03 2019 *)
%o A064335 (PARI) { s=6; for (n=0, 100, if (n, s*=2*n*(2*n - 1)); a=s/(n + 2); write("b064335.txt", n, " ", a) ) } \\ _Harry J. Smith_, Sep 12 2009
%o A064335 (PARI) a(n) = 6*(2*n)!/(n+2); \\ _Michel Marcus_, Jun 24 2018
%o A064335 (Magma) [6*Factorial(2*n)/(n+2): n in [0..20]]; // _G. C. Greubel_, May 03 2019
%o A064335 (Sage) [6*factorial(2*n)/(n+2) for n in (0..20)] # _G. C. Greubel_, May 03 2019
%o A064335 (GAP) List([0..20], n-> 6*Factorial(2*n)/(n+2)); # _G. C. Greubel_, May 03 2019
%Y A064335 Cf. A060593.
%K A064335 nonn
%O A064335 0,1
%A A064335 _Karol A. Penson_, Sep 13 2001