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 A113259 Expansion of psi(x)^5 / psi(x^5) - 25*x^2 * psi(x) * psi(x^5)^3 in powers of x where psi() is a Ramanujan theta function. 1
 1, 5, -15, -10, 25, 5, 30, -30, -55, 35, -15, 60, -50, -60, 90, -10, 105, -80, -105, 100, 25, 60, -180, -110, 110, 5, 180, -100, -150, 150, 30, 160, -215, -120, 240, -30, 175, -180, -300, 120, -55, 210, -180, -210, 300, 35, 330, -230, -210, 215, -15, 160, -300, -260, 300, 60, 330, -200, -450 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700). REFERENCES B. C. Berndt, Ramanujan's Notebooks Part III, Springer-Verlag, see p. 249 Entry 8(iv). LINKS Michael Somos, Introduction to Ramanujan theta functions Eric Weisstein's World of Mathematics, Ramanujan Theta Functions FORMULA G.f.: 1 + 5*( Sum_{k>0} (k*x^k / (1 + x^k)) * Kronecker(5, k) ). a(n) = 5 * A113260(n) if n>0. EXAMPLE G.f. = 1 + 5*x - 15*x^2 - 10*x^3 + 25*x^4 + 5*x^5 + 30*x^6 - 30*x^7 - 55*x^8 + ... MATHEMATICA a[ n_] := If[ n < 1, Boole[n == 0], -5 DivisorSum[ n, # KroneckerSymbol[ 5, #] (-1)^(n/#) &]]; (* Michael Somos, Sep 07 2018 *) PROG (PARI) {a(n) = if( n<1, n==0, -5 * sumdiv(n, d, d * kronecker(5, d) * (-1)^(n/d)))}; CROSSREFS Cf. A113260. Sequence in context: A290829 A290837 A302841 * A298265 A309620 A291794 Adjacent sequences:  A113256 A113257 A113258 * A113260 A113261 A113262 KEYWORD sign AUTHOR Michael Somos, Oct 20 2005 STATUS approved

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Last modified May 6 16:03 EDT 2021. Contains 343586 sequences. (Running on oeis4.)