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 A132968 Expansion of chi(-q) * chi(-q^15) / (chi(-q^6) * chi(-q^10)) in powers of q where chi() is a Ramanujan theta function. 4
 1, -1, 0, -1, 1, -1, 2, -2, 2, -3, 4, -4, 5, -6, 6, -9, 11, -10, 14, -16, 17, -22, 24, -26, 32, -37, 40, -47, 54, -58, 70, -80, 84, -100, 112, -122, 143, -158, 172, -198, 222, -242, 274, -306, 332, -379, 422, -454, 515, -569, 620, -698, 766, -834, 932, -1028 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,7 COMMENTS Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700). LINKS Seiichi Manyama, Table of n, a(n) for n = 0..10000 Michael Somos, Introduction to Ramanujan theta functions Michael Somos, A Remarkable eta-product Identity Eric Weisstein's World of Mathematics, Ramanujan Theta Functions FORMULA Expansion of eta(q) * eta(q^12) * eta(q^15) * eta(q^20) / (eta(q^2) * eta(q^6) * eta(q^10) * eta(q^30)) in powers of q. Euler transform of period 60 sequence [-1, 0, -1, 0, -1, 1, -1, 0, -1, 1, -1, 0, -1, 0, -2, 0, -1, 1, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 2, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 1, -1, 0, -2, 0, -1, 0, -1, 1, -1, 0, -1, 1, -1, 0, -1, 0, -1, 0, ...]. G.f. is a period 1 Fourier series which satisfies f(-1 / (60 t)) = g(t) where q = exp(2 Pi i t) and g() is the g.f. for A132967. G.f.: Product_{k>0} (1 + x^(6*k)) * (1 + x^(10*k)) / ( (1 + x^k) * (1 + x^(15*k)) ). a(n) = - A132967(n) unless n=0. a(n) ~ (-1)^n * exp(2*Pi*sqrt(n/15)) / (4 * 15^(1/4) * n^(3/4)). - Vaclav Kotesovec, Nov 07 2015 EXAMPLE G.f. = 1 - q - q^3 + q^4 - q^5 + 2*q^6 - 2*q^7 + 2*q^8 - 3*q^9 + 4*q^10 - ... MATHEMATICA nmax = 60; CoefficientList[Series[Product[(1 + x^(6*k)) * (1 + x^(10*k)) / ( (1 + x^k) * (1 + x^(15*k))), {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Nov 07 2015 *) PROG (PARI) {a(n) = my(A); if( n<0, 0, A = x*O(x^n); polcoeff( eta(x + A) * eta(x^12 + A) * eta(x^15 + A) * eta(x^20 + A) / (eta(x^2 + A) * eta(x^6 + A) * eta(x^10 + A) * eta(x^30 + A)), n))}; CROSSREFS Cf. A132967. Sequence in context: A053254 A067357 A051059 * A132967 A029075 A029052 Adjacent sequences:  A132965 A132966 A132967 * A132969 A132970 A132971 KEYWORD sign AUTHOR Michael Somos, Sep 02 2007 STATUS approved

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Last modified August 4 21:21 EDT 2021. Contains 346455 sequences. (Running on oeis4.)