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 A129449 Expansion of psi(-x) * psi(-x^3) in powers of x where psi() is a Ramanujan theta function. 3
 1, -1, 0, -2, 1, 0, 2, 0, 0, -2, 2, 0, 1, -1, 0, -2, 0, 0, 2, -2, 0, -2, 0, 0, 3, 0, 0, 0, 2, 0, 2, -2, 0, -2, 0, 0, 2, -1, 0, -2, 1, 0, 0, 0, 0, -4, 2, 0, 2, 0, 0, -2, 0, 0, 2, -2, 0, 0, 2, 0, 1, 0, 0, -2, 2, 0, 4, 0, 0, -2, 0, 0, 0, -3, 0, -2, 0, 0, 2, 0, 0, -2, 0, 0, 3, -2, 0, -2, 0, 0, 2, -2, 0, 0, 2, 0, 2, 0, 0, -2, 2, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700). Number 53 of the 74 eta-quotients listed in Table I of Martin (1996). LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 Y. Martin, Multiplicative eta-quotients, Trans. Amer. Math. Soc. 348 (1996), no. 12, 4825-4856, see page 4852 Table I. Michael Somos, Introduction to Ramanujan theta functions Eric Weisstein's World of Mathematics, Ramanujan Theta Functions FORMULA Expansion of q^(-1/2) * eta(q) * eta(q^3) * eta(q^4) * eta(q^12) / (eta(q^2) * eta(q^6)) in powers of q. Euler transform of period 12 sequence [ -1, 0, -2, -1, -1, 0, -1, -1, -2, 0, -1, -2, ...]. a(n) = b(2*n + 1) where b() is multiplicative with b(2^e) = 0^e, b(3^e) = (-1)^e, b(p^e) = (1 + (-1)^e) / 2 if p == 5, 11 (mod 12), b(p^e) = e+1 if p == 1 (mod 12), b(p^e) = (-1)^e * (e+1) if p == 7 (mod 12). G.f. is a period 1 Fourier series which satisfies f(-1 / (48 t)) = 48^(1/2) (t/i) f(t) where q = exp(2 Pi i t). a(n) = (-1)^n * A033762(n). a(2*n) = A112604(n). a(2*n + 1) = -A112605(n). a(3*n) = A129451(n). a(3*n + 1) = -a(n). a(3*n + 2) = 0. a(4*n) = A112606(n). a(4*n + 1) = - A112608(n). a(4*n + 2) = 2 * A112607(n). a(4*n + 3) = - 2 * A112609(n). a(6*n) = A123884(n). a(6*n + 3) = -2 * A121361(n). EXAMPLE G.f. = 1 - x - 2*x^3 + x^4 + 2*x^6 - 2*x^9 + 2*x^10 + x^12 - x^13 - 2*x^15 + ... G.f. = q - q^3 - 2*q^7 + q^9 + 2*q^13 - 2*q^19 + 2*q^21 + q^25 - q^27 + ... MATHEMATICA a[ n_] := SeriesCoefficient[ EllipticTheta[ 2, Pi/4, x^(1/2)] EllipticTheta[ 2, Pi/4, x^(3/2)] / (2 x^(1/2)), {x, 0, n}]; (* Michael Somos, Jul 09 2015 *) a[ n_] := With[ {m = 2 n + 1}, If[ m < 1, 0, Sum[ KroneckerSymbol[ 12, d] KroneckerSymbol[ -4, m/d], {d, Divisors[ m]}]]]; (* Michael Somos, Jul 09 2015 *) PROG (PARI) {a(n) = if( n<0, 0, n = 2*n + 1; sumdiv( n, d, kronecker( -4, d) * kronecker( 12, n/d)))}; (PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x + A) * eta(x^3 + A) * eta(x^4 + A) * eta(x^12 + A)/ (eta(x^2 + A) * eta(x^6 + A)), n))}; CROSSREFS Cf. A033762, A112604, A113605, A112606, A112608, A112609, A121361, A123884, A129451. Sequence in context: A058677 A262780 A033762 * A033798 A033792 A033768 Adjacent sequences:  A129446 A129447 A129448 * A129450 A129451 A129452 KEYWORD sign AUTHOR Michael Somos, Apr 16 2007 STATUS approved

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Last modified September 25 18:49 EDT 2021. Contains 347659 sequences. (Running on oeis4.)