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Expansion of Product_{k>=0} (1 + x^(3^k))^3.
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%I #10 Jul 15 2024 10:23:04

%S 1,3,3,4,9,9,6,9,9,7,12,12,13,27,27,18,27,27,15,18,18,15,27,27,18,27,

%T 27,16,21,21,19,36,36,24,36,36,25,39,39,40,81,81,54,81,81,45,54,54,45,

%U 81,81,54,81,81,42,45,45,33,54,54,36,54,54,33,45,45,42,81,81,54,81,81,45,54,54,45,81,81,54,81,81

%N Expansion of Product_{k>=0} (1 + x^(3^k))^3.

%F G.f. A(x) satisfies A(x) = (1 + x)^3 * A(x^3).

%o (PARI) my(N=90, x='x+O('x^N)); Vec(prod(k=0, logint(N, 3), 1+x^3^k)^3)

%Y Cf. A039966, A120880.

%K nonn

%O 0,2

%A _Seiichi Manyama_, Jul 14 2024