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A093065
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Expansion of (eta(q^3)eta(q^15)/(eta(q)eta(q^5)))^2 in powers of q.
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0
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0, 1, 2, 5, 8, 16, 28, 48, 78, 124, 194, 302, 454, 682, 996, 1457, 2096, 2993, 4226, 5920, 8228, 11373, 15580, 21246, 28740, 38731, 51872, 69155, 91716, 121105, 159208, 208512, 271894, 353338, 457336, 590124, 758792, 972677, 1242896, 1583576
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OFFSET
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0,3
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COMMENTS
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Euler transform of period 15 sequence [2,2,0,2,4,0,2,2,0,4,2,0,2,2,0,...].
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LINKS
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FORMULA
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G.f. A(x) satisfies 0=f(A(x), A(x^2)) where f(u, v)=u^3+v^3-4uv(u+v)-9u^2v^2-uv.
a(n) ~ exp(4*Pi*sqrt(n/15)) / (9*sqrt(2)*15^(1/4)*n^(3/4)). - Vaclav Kotesovec, Jul 11 2016
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MATHEMATICA
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nmax = 50; CoefficientList[Series[x*Product[((1-x^(3*k)) * (1-x^(15*k)) / ((1-x^k) * (1-x^(5*k))))^2, {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Jul 11 2016 *)
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PROG
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(PARI) {a(n)=local(A); if(n<1, 0, n--; A=x*O(x^n); polcoeff((eta(x^3+A)*eta(x^15+A)/eta(x+A)/eta(x^5+A))^2, n))}
(PARI) {a(n)=local(A, u, v); if(n<0, 0, A=x; for(k=2, n, u=A+x*O(x^k); v=subst(u, x, x^2); A-=x^k*polcoeff(u^3+v^3-4*u*v*(u+v)-9*u^2*v^2-u*v, k+2)/2); polcoeff(A, n))}
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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