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%I #14 Mar 08 2020 00:24:12
%S 2,36,1320,84000,8285760,1173553920,226040855040,56865153945600,
%T 18112111963545600,7125892746964992000,3394344333441245184000,
%U 1925382105537337294848000,1282520788685931213619200000,991363455147400701817651200000,880169729965718014490443776000000
%N a(n) = (2n)!*Sum_{i=1..n} 1/i.
%H I. Nemes et al., <a href="https://www.jstor.org/stable/2975078">How to do Monthly problems with your computer</a>, Amer. Math. Monthly, 104 (1997), 505-519.
%t Table[(2n)!HarmonicNumber[n],{n,20}] (* _Harvey P. Dale_, Sep 27 2013 *)
%o (PARI) a(n) = (2*n)!*sum(k=1, n, 1/k); \\ _Michel Marcus_, Jul 11 2018
%Y Cf. A000254, A101613.
%K nonn
%O 1,1
%A _N. J. A. Sloane_
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