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 A215556 Expansion of q * psi(-q) * phi(q) * psi(-q^7) in powers of q where phi(), psi() are Ramanujan theta functions. 2
 1, 1, -2, -1, 0, -2, 1, -1, -1, 4, 2, 2, 0, -1, 2, 1, -2, -3, -2, 0, 0, -4, -2, 2, 1, 0, 4, -1, 0, 2, -4, 1, 0, 2, 0, 1, 0, 2, 2, -4, 2, 0, 2, -2, 0, 2, 0, -2, 1, -1, -4, 0, 0, 4, -4, 1, -2, -2, 2, -2, 0, 0, -1, -1, 2, -4, -2, 2, 0, 0, 0, 3, 2, -2, 2, 2, 0, 6 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700). LINKS G. C. Greubel, Table of n, a(n) for n = 1..5000 Michael Somos, Introduction to Ramanujan theta functions Eric Weisstein's World of Mathematics, Ramanujan Theta Functions FORMULA Expansion of eta(q^2)^4 * eta(q^7) * eta(q^28) / (eta(q) * eta(q^4) * eta(q^14)) in powers of q. Euler transform of period 28 sequence [ 1, -3, 1, -2, 1, -3, 0, -2, 1, -3, 1, -2, 1, -3, 1, -2, 1, -3, 1, -2, 0, -3, 1, -2, 1, -3, 1, -3, ...]. G.f. is a period 1 Fourier series which satisfies f(-1 / (28 t)) = 392^(1/2) (t/i)^(3/2) g(t) where q = exp(2 Pi i t) and g() is the g.f. for A159813. a(7*n) = A159813(n). EXAMPLE G.f. = q + q^2 - 2*q^3 - q^4 - 2*q^6 + q^7 - q^8 - q^9 + 4*q^10 + 2*q^11 + 2*q^12 + ... MATHEMATICA a[ n_] := SeriesCoefficient[ EllipticTheta[ 3, 0, q] EllipticTheta[ 2, Pi/4, q^(1/2)] EllipticTheta[ 2, Pi/4, q^(7/2)] / 2, {q, 0, n}]; (* Michael Somos, Aug 27 2015 *) PROG (PARI) {a(n) = my(A); if( n<1, 0, n--; A = x * O(x^n); polcoeff( eta(x^2 + A)^4 * eta(x^7 + A) * eta(x^28 + A) / (eta(x + A) * eta(x^4 + A) * eta(x^14 + A)), n))}; CROSSREFS Cf. A159813. Sequence in context: A270657 A270658 A117278 * A140082 A330714 A343640 Adjacent sequences:  A215553 A215554 A215555 * A215557 A215558 A215559 KEYWORD sign AUTHOR Michael Somos, Aug 15 2012 STATUS approved

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Last modified January 26 05:13 EST 2022. Contains 350572 sequences. (Running on oeis4.)