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%I #7 Oct 07 2023 08:48:40
%S 1,5,315,555713,47705305725,305469864195354625,
%T 207095306530955763265880535,20017329298655447986400838721630926977,
%U 357361761140807273279996172600335233468472149678425,1481824279740988988264353294673429995981921700740921435758587890625
%N a(n) = Product_{k=1..n} (k^n + (k-1)^n).
%F a(n) = (n!)^n * Product_{k=1..n} (1 + (1 - 1/k)^n).
%F a(n) ~ n!^n * d^n, where d = exp(Integral_{x=0..1} log(1 + exp(-1/x)) dx) = 1.14183186235785012136459060138978468902610644657603999829892450823456733...
%F a(n) ~ (2*Pi)^(n/2) * d^n * n^(n*(2*n+1)/2) / exp(n^2 - 1/12).
%t Table[Product[k^n + (k-1)^n, {k, 1, n}], {n, 1, 10}]
%Y Cf. A036740, A323575, A323588, A323589, A366306.
%K nonn
%O 1,2
%A _Vaclav Kotesovec_, Oct 06 2023