A393555 - OEIS

%I #8 Feb 21 2026 13:35:20

%S 1,2,4,10,18,32,60,100,164,276,436,680,1070,1624,2440,3672,5402,7880,

%T 11484,16476,23472,33360,46880,65488,91212,125958,173048,237012,

%U 322432,436680,589604,791720,1058948,1412208,1874708,2479992,3271596,4299056,5631536,7357804

%N Expansion of Product_{i>=1, j>=0} (1 + x^(i * 3^j)) / (1 - x^(i * 3^j)).

%C Convolution of A327726 and A173241.

%H Vaclav Kotesovec, <a href="/A393555/b393555.txt">Table of n, a(n) for n = 0..10000</a>

%F log(a(n)) ~ Pi*sqrt(3*n/2).

%t nmax = 50; CoefficientList[Series[Product[((1 + x^k)/(1 - x^k))^(IntegerExponent[k, 3] + 1), {k, 1, nmax}], {x, 0, nmax}], x]

%t nmax = 50; CoefficientList[Series[Product[(1+x^(i*3^j))/(1-x^(i*3^j)), {i, 1, nmax}, {j, 0, Log[nmax]/Log[3]+1}], {x, 0, nmax}], x]

%Y Cf. A327727, A393556, A393557, A393558, A393559.

%Y Cf. A327726, A173241.

%K nonn

%O 0,2

%A _Vaclav Kotesovec_, Feb 21 2026