A257657 - OEIS

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A257657

Expansion of f(-x, -x) * f(-x^6, -x^6) / f(x, x^2) in powers of x where f(,) is Ramanujan's general theta function.

1, -3, 2, 1, -1, -1, 3, -1, 0, -2, -2, 2, 1, -3, 3, 4, -1, -3, 1, 0, -1, -2, 0, 3, 1, -6, 2, 4, -4, -1, 4, 2, -1, -3, 0, 5, -1, -9, 5, 7, -4, -7, 4, 5, -3, -4, 0, 8, -1, -13, 4, 11, -7, -7, 7, 6, -1, -10, 0, 14, -1, -15, 8, 15, -10, -14, 8, 11, -7, -13, 2, 17

(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).

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..2500

Michael Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

FORMULA

Expansion of q^(1/24) * eta(q)^3 * eta(q^6)^3 / (eta(q^2)^2 * eta(q^3)^2 * eta(q^12)) in powers of q.

Euler transform of period 12 sequence [ -3, -1, -1, -1, -3, -2, -3, -1, -1, -1, -3, -1, ...].

a(n) = 2 * A260413(n) - A053250(n).

EXAMPLE

G.f. = 1 - 3*x + 2*x^2 + x^3 - x^4 - x^5 + 3*x^6 - x^7 - 2*x^9 - 2*x^10 + ...

G.f. = 1/q - 3*q^23 + 2*q^47 + q^71 - q^95 - q^119 + 3*q^143 - q^167 + ...

MATHEMATICA

a[ n_] := SeriesCoefficient[ QPochhammer[ x, x^2]^2 QPochhammer[ x] QPochhammer[ -x^3] / QPochhammer[ x^3], {x, 0, n}];

PROG

(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x + A)^3 * eta(x^6 + A)^3 / (eta(x^2 + A)^2 * eta(x^3 + A)^2 * eta(x^12 + A)), n))};

CROSSREFS

Cf. A053250, A260413.

Sequence in context: A210650 A218754 A079948 * A339584 A106689 A348177

Adjacent sequences: A257654 A257655 A257656 * A257658 A257659 A257660

KEYWORD

sign

AUTHOR

Michael Somos, Jul 26 2015

STATUS

approved