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G.f.: Sum_{k>=0} x^(k*(k+1)/2) * Product_{j=1..k} 1/(1 - x^j)^4.
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%I #5 Oct 02 2024 12:30:38

%S 1,1,4,11,24,49,93,173,310,549,946,1608,2676,4391,7083,11283,17724,

%T 27539,42309,64382,97052,145092,215161,316737,462980,672310,970154,

%U 1391667,1984999,2816059,3974475,5581789,7802161,10856466,15040941,20751416,28515375,39033040

%N G.f.: Sum_{k>=0} x^(k*(k+1)/2) * Product_{j=1..k} 1/(1 - x^j)^4.

%F a(n) ~ r^(1/8) * (log(r)^2 + 8*polylog(2, 1-r)) * exp(sqrt(2*(log(r)^2 + 8*polylog(2, 1-r))*n)) / (2^(7/2) * Pi^2 * sqrt(1 + 3*r) * n^(3/2)), where r = 0.2755080409994... is the smallest real root of the equation r = (1-r)^4.

%t nmax = 40; CoefficientList[Series[Sum[x^(k*(k+1)/2)/Product[1-x^j, {j, 1, k}]^4, {k, 0, Sqrt[2*nmax]}], {x, 0, nmax}], x]

%Y Cf. A000009, A143184, A376707.

%K nonn

%O 0,3

%A _Vaclav Kotesovec_, Oct 02 2024