A262090 Expansion of f(x^3, x^21) / f(-x^2, -x^4) where f(, ) is the Ramanujan general theta function.

1, 0, 1, 1, 2, 1, 3, 2, 5, 3, 7, 5, 11, 7, 15, 11, 22, 15, 30, 22, 42, 31, 56, 43, 77, 58, 101, 80, 135, 106, 177, 142, 232, 187, 299, 246, 388, 319, 495, 415, 634, 532, 803, 683, 1017, 869, 1277, 1103, 1605, 1390, 2000, 1751, 2492, 2189, 3087, 2733, 3819

Offset

0,5

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

Euler transform of period 48 sequence [ 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 1, 0, 0, ...].

a(n) = - A143067(2*n + 3).

Example

G.f. = 1 + x^2 + x^3 + 2*x^4 + x^5 + 3*x^6 + 2*x^7 + 5*x^8 + 3*x^9 + ...
G.f. = q^77 + q^173 + q^221 + 2*q^269 + q^317 + 3*q^365 + 2*q^413 + ...

Mathematica

a[ n_] := SeriesCoefficient[ QPochhammer[ -x^3, x^24] QPochhammer[ -x^21, x^24] QPochhammer[ x^24] / QPochhammer[ x^2], {x, 0, n}];

Prog

(PARI) {a(n) = if( n<0, 0, A = x * O(x^n); polcoeff( subst( prod(k=1, n\3, 1 - x^k * [1, 1, 0, 0, 0, 0, 0, 1][k%8 + 1], 1 + x * O(x^(n\3))), x, -x^3) / eta(x^2 + x * O(x^n)), n))};

Crossrefs

Cf. A143067.

Sequence in context: A008731 A114209 A132091 * A239881 A051792 A053602

Adjacent sequences: A262087 A262088 A262089 * A262091 A262092 A262093

Keyword

nonn

Author

Michael Somos, Sep 10 2015

Status

approved