%I #8 Feb 28 2024 18:04:49
%S 1,6,18,1170,-1890,133326,101250,20498994,-164656314,3778220862,
%T -28085954094,771567716970,-10691904063114,183594050113518,
%U -2711145260068326,49416883617381354,-789899109743435994,13176840267952166070,-216403389726994588086,3681309971143060236810
%N a(n) = 3^(2*n) * [x^n] Product_{k>=1} (1 + 2*x^k)^(1/3).
%F G.f.: Product_{k>=1} (1 + 2*(9*x)^k)^(1/3).
%F a(n) ~ (-1)^(n+1) * c * 18^n / n^(4/3), where c = QPochhammer(-1/2)^(1/3) / (3*Gamma(2/3)) = 0.2623638446186535909018671540030519...
%t nmax = 20; CoefficientList[Series[Product[(1 + 2*x^k), {k, 1, nmax}]^(1/3), {x, 0, nmax}], x] * 3^(2*Range[0, nmax])
%t nmax = 20; CoefficientList[Series[Product[(1 + 2*(9*x)^k), {k, 1, nmax}]^(1/3), {x, 0, nmax}], x]
%t nmax = 20; CoefficientList[Series[(QPochhammer[-2, x]/3)^(1/3), {x, 0, nmax}], x] * 3^(2*Range[0, nmax])
%Y Cf. A032302, A370715.
%Y Cf. A075900, A300581, A304961, A327550.
%K sign
%O 0,2
%A _Vaclav Kotesovec_, Feb 27 2024