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Expansion of Product_{n>=1} (1 + (9*x)^n)^(1/3).
9

%I #11 Feb 28 2024 18:11:06

%S 1,3,18,369,1674,31428,266733,3012714,19924299,319970007,2688208641,

%T 27248985549,248061612240,2597556114648,25367004717831,

%U 289880288735373,2289952155529719,23895509092285545,252143223166599723,2308267172943599733,22389894059315522040

%N Expansion of Product_{n>=1} (1 + (9*x)^n)^(1/3).

%C In general, for h>=1, if g.f. = Product_{k>=1} (1 + (h^2*x)^k)^(1/h), then a(n) ~ h^(2*n) * exp(Pi*sqrt(n/(3*h))) / (2^((3*h + 1)/(2*h)) * 3^(1/4) * h^(1/4) * n^(3/4)).

%H Vaclav Kotesovec, <a href="/A303074/b303074.txt">Table of n, a(n) for n = 0..1000</a>

%F a(n) ~ 3^(2*n - 1/2) * exp(sqrt(n)*Pi/3) / (2^(5/3) * n^(3/4)).

%t CoefficientList[Series[(QPochhammer[-1, 9*x]/2)^(1/3), {x, 0, 20}], x]

%Y Cf. A271236, A298994, A303342, A370739.

%K nonn

%O 0,2

%A _Vaclav Kotesovec_, Apr 18 2018