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A214316
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Expansion of psi(x)^2 - 5 * x * psi(x^5)^2 in powers of x where psi() is a Ramanujan theta function.
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3
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1, -3, 1, 2, 2, 0, -7, 2, 0, 2, 2, -3, 1, 2, 0, 2, -6, 0, 2, 0, 1, -6, 2, 0, 2, 2, 0, 2, 2, 2, 1, -11, 0, 0, 2, 0, -6, 2, 2, 2, 0, 0, 3, 2, 0, 2, -6, 0, 2, 2, 0, -6, 0, 0, 0, 4, -7, 2, 2, 0, 2, -3, 0, 0, 2, 2, -6, 2, 0, 2, 2, 0, 3, 2, 0, 0, -6, 0, 2, 2, 0
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OFFSET
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0,2
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COMMENTS
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REFERENCES
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S. Cooper, On Ramanujan's function k(q)=r(q)r^2(q^2), Ramanujan J., 20 (2009), 311-328; see p. 314 eq. (2.7)
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LINKS
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FORMULA
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Expansion of f(-x) * phi(-x) / chi(-x^5) in powers of x where phi(), chi(), f() are Ramanujan theta functions.
Expansion of q^(-1/4) * eta(q)^3 * eta(q^10) / (eta(q^2) * eta(q^5)) in powers of q.
Euler transform of period 10 sequence [ -3, -2, -3, -2, -2, -2, -3, -2, -3, -2, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (40 t)) = 10 (t/i) g(t) where q = exp(2 Pi i t) and g(t) is g.f. for A094247.
a(9*n + 5) = a(9*n + 8) = 0. a(9*n + 2) = a(n).
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EXAMPLE
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G.f. = 1 - 3*x + x^2 + 2*x^3 + 2*x^4 - 7*x^6 + 2*x^7 + 2*x^9 + 2*x^10 - 3*x^11 + ...
G.f. = q - 3*q^5 + q^9 + 2*q^13 + 2*q^17 - 7*q^25 + 2*q^29 + 2*q^37 + 2*q^41 + ...
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MATHEMATICA
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a[ n_] := SeriesCoefficient[ QPochhammer[ x]^3 QPochhammer[ x^10] / (QPochhammer[ x^2] QPochhammer[ x^5]), {x, 0, n}]
a[ n_] := SeriesCoefficient[ (EllipticTheta[ 2, 0, q^2]^2 - 5 EllipticTheta[ 2, 0, q^10]^2) / 4, {q, 0, 4 n + 1}]
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PROG
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(PARI) {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x + A)^3 * eta(x^10 + A) / (eta(x^2 + A) * eta(x^5 + A)), n))}
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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