A186742 Expansion of f(x, x^11) in powers of x where f(, ) is Ramanujan's general theta function.

1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Offset

0,1

Comments

Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700).

Links

Seiichi Manyama, Table of n, a(n) for n = 0..10000

Michael Somos, Introduction to Ramanujan theta functions, 2019.

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions.

Formula

Euler transform of period 24 sequence [1, -1, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1, 1, 0, 0, 0, 0, 0, 0, 0, 0, -1, 1, -1, ...].

a(n) is the characteristic function of A195818. a(n) = max( 0, -A010815(n + 1)).

G.f.: Sum_{k in Z} x^(6*k^2 - 5*k) = Product_{k>0} (1 + x^(12*k - 11)) * (1 + x^(12*k - 1)) * (1 - x^(12*k)).

Expansion of (f(x, x^2) - f(-x, -x^2)) / (2*x) in powers of x. - Michael Somos, Aug 28 2017

Sum_{k=1..n} a(k) ~ sqrt(2*n/3). - Amiram Eldar, Jan 13 2024

Example

G.f. = 1 + x + x^11 + x^14 + x^34 + x^39 + x^69 + x^76 + x^116 + x^125 + ...
G.f. = q^25 + q^49 + q^289 + q^361 + q^841 + q^961 + q^1681 + q^1849 + ...

Mathematica

a[ n_] := With[{m = Sqrt[24 n + 25]}, If[ n >= 0 && IntegerQ @ m, Boole[ Mod[m, 12] == 5 || Mod[m, 12] == 7], 0]]; (* Michael Somos, Aug 28 2017 *)
a[ n_] := SeriesCoefficient[ QPochhammer[ x^12] QPochhammer[ -x^1, x^12] QPochhammer[ -x^11, x^12], {x, 0, n}]; (* Michael Somos, Aug 28 2017 *)

Prog

(PARI) {a(n) = my(m); n++; if( !issquare( 24*n + 1, &m), 0, m%12 == 5 || m%12 == 7)};
(PARI) {a(n) = my(A); n = 3*n + 3; if( n<0, 0, A = x * O(x^n); polcoeff( (eta(x^2 + A)^2 / eta(x + A) - eta(x^3 + A) - x * eta(x^18 + A)^2 / eta(x^9 + A)) / 2, n))}; /* Michael Somos, Aug 28 2017 */

Crossrefs

Cf. A010815, A195818.

Cf. A000122, A000700, A010054, A121373.

Sequence in context: A016412 A256434 A247133 * A016365 A016426 A014020

Adjacent sequences: A186739 A186740 A186741 * A186743 A186744 A186745

Keyword

nonn

Author

Michael Somos, Jan 21 2012

Status

approved