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%I #31 Feb 28 2024 02:34:22
%S 0,1,6,66,1200,32880,1270080,65862720,4418426880,372523898880,
%T 38569208832000,4811724352512000,712008517828608000,
%U 123312192439468032000,24712050750746591232000,5674212235766262988800000,1479958528399750515916800000,435149988031383614993203200000
%N a(n) = n!^2*(Sum_{k=1..n} 1/k).
%C For n>=1, a(n) is the number of vertices of the harmonic polytope. See Ardila and Escobar.
%H Federico Ardila and Laura Escobar, <a href="https://arxiv.org/abs/2006.03078">The harmonic polytope</a>, arXiv:2006.03078 [math.CO], 2020.
%F a(n) = A000142(n)*A000254(n).
%o (PARI) a(n) = n!^2*sum(k=1, n, 1/k);
%Y Cf. A000142, A000254.
%K nonn
%O 0,3
%A _Michel Marcus_, Jun 08 2020