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%I #19 Oct 13 2017 05:14:27
%S 1,1,3,5,11,18,34,55,95,150,244,376,588,885,1340,1978,2922,4235,6130,
%T 8745,12442,17501,24533,34075,47156,64756,88594,120420,163075,219595,
%U 294652,393407,523468,693465,915681,1204329,1579087,2063035,2687440,3489365,4518083,5832448
%N G.f.: (Product_{j>=1} 1/(1-q^j)^2 + Product_{j>=1} 1/(1-q^(2*j)))/2.
%H Roland Bacher, P. De La Harpe, <a href="https://hal.archives-ouvertes.fr/hal-01285685/document">Conjugacy growth series of some infinitely generated groups</a>, hal-01285685v2, 2016.
%F a(n) ~ exp(2*Pi*sqrt(n/3)) / (8 * 3^(3/4) * n^(5/4)). - _Vaclav Kotesovec_, Oct 13 2017
%t CoefficientList[Series[(1/QPochhammer[x, x]^2 + 1/QPochhammer[x^2, x^2])/2, {x, 0, 50}], x] (* _Vaclav Kotesovec_, Oct 13 2017 *)
%o (PARI) nn = 50; Vec((prod(j=1, nn, 1/(1-q^j)^2) + prod(j=1, nn, 1/(1-q^(2*j))))/2 + O(q^nn)) \\ _Michel Marcus_, Oct 13 2017
%K nonn
%O 0,3
%A _N. J. A. Sloane_, Jan 22 2017
%E More terms from _Ilya Gutkovskiy_, Feb 02 2017
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