A132972 Expansion of chi(q)^3 / chi(q^3) in powers of q where chi() is a Ramanujan theta function.
1, 3, 3, 3, 6, 9, 12, 15, 21, 30, 36, 45, 60, 78, 96, 117, 150, 189, 228, 276, 342, 420, 504, 603, 732, 885, 1050, 1245, 1488, 1773, 2088, 2454, 2901, 3420, 3996, 4662, 5460, 6378, 7404, 8583, 9972, 11565, 13344, 15378, 17748, 20448, 23472, 26910, 30876
Offset: 0
Keywords
Examples
G.f. = 1 + 3*q + 3*q^2 + 3*q^3 + 6*q^4 + 9*q^5 + 12*q^6 + 15*q^7 + 21*q^8 + ...
Links
- G. C. Greubel, Table of n, a(n) for n = 0..1000
- Michael Somos, Introduction to Ramanujan theta functions
- Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
Programs
-
Mathematica
nmax = 60; CoefficientList[Series[Product[(1 + x^(2*k-1))^3 / (1 + x^(6*k-3)), {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Sep 08 2015 *) a[ n_] := SeriesCoefficient[ QPochhammer[ -q, q^2]^3 / QPochhammer[ -q^3, q^6], {q, 0, n}]; (* Michael Somos, Oct 31 2015 *) -
PARI
{a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A)^6 * eta(x^3 + A) * eta(x^12 + A) / (eta(x + A)^3 * eta(x^4 + A)^3 * eta(x^6 + A)^2), n))};
Formula
Expansion of eta(q^2)^6 * eta(q^3) * eta(q^12) / (eta(q)^3 * eta(q^4)3 * eta(q^12)) in powers of q.
Euler transform of period 12 sequence [ 3, -3, 2, 0, 3, -2, 3, 0, 2, -3, 3, 0, ...].
G.f. A(x) satisfies 0 = f(A(x), A(x^2)) where f(u, v) = (2 + u*v) * (u*v - 1)^3 - (u - u^4) * (v - v^4).
G.f. A(x) satisfies 0 = f(A(x), A(x^3)) where f(u, v) = u * (4 - 2*u + u^2) - v^3 * (1 + u + u^2).
G.f. A(x) satisfies 0 = f(A(x), A(x^2), A(x^3), A(x^6)) where f(u1, u2, u3, u6) = (2 + u1 * u2) - u3 * u6 * (1 + u1 + u2).
G.f. is a period 1 Fourier series which satisfies f(-1/(144*t)) = g(t) where q = exp(2 Pi i t) and g() is the g.f. for A062244.
G.f.: Product_{k>0} (1 + x^(2*k-1))^3 / (1 + x^(6*k-3)).
a(n) = 3 * A132975(n) unless n=0.
Empirical: Sum_{n>=1} exp(-Pi)^(n-1)*a(n) = (-2 + 2*sqrt(3))^(1/3). - Simon Plouffe, Feb 20 2011
a(n) ~ exp(2*Pi*sqrt(n)/3) / (2*sqrt(3)*n^(3/4)). - Vaclav Kotesovec, Sep 08 2015
It appears that the g.f. A(x) = F(x)^3, where F(x) = exp( Sum_{n >= 0} x^(3*n+1)/((3*n + 1)*(1 - (-1)^(n+1)*x^(3*n+1))) + x^(3*n+2)/((3*n + 2)*(1 - (-1)^n*x^(3*n + 2))) ). Cf. A273845. - Peter Bala, Dec 23 2021
Comments