M. Michael Somos, <a href="/A010815/a010815.txt">Introduction to Ramanujan theta functions</a>
M. Michael Somos, <a href="/A010815/a010815.txt">Introduction to Ramanujan theta functions</a>
M. Somos, <a href="http://somos.crg4.comA010815/multiqa010815.htmltxt
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G. C. Greubel, <a href="/A128517/b128517.txt">Table of n, a(n) for n = -1..1000</a>
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Vaclav Kotesovec, <a href="http://arxiv.org/abs/1509.08708">A method of finding the asymptotics of q-series based on the convolution of generating functions</a>, arXiv:1509.08708 [math.CO], Sep 30 2015
a(n) ~ exp(2*Pi*sqrt(2*n)/3) / (2^(3/4) * sqrt(3) * n^(3/4)). - Vaclav Kotesovec, Oct 13 2015
nmax=60; CoefficientList[Series[Product[((1+x^k) / (1+x^(9*k)))^3, {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Oct 13 2015 *)
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(PARI) {a(n) = my(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( (eta(x^2 + A) * eta(x^9 + A) / (eta(x + A) * eta(x^18 + A)))^3, n))};
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