A258939 - OEIS

A258939

Expansion of f(-x^3, -x^5) * f(x^3, x^13) / (f(-x, -x^2) * f(-x^8, -x^16)) in powers of x where f(, ) is Ramanujan's general theta function.

1, 1, 2, 3, 5, 6, 9, 12, 17, 22, 30, 38, 51, 64, 83, 104, 133, 165, 208, 256, 319, 390, 481, 584, 715, 863, 1047, 1258, 1517, 1812, 2172, 2584, 3080, 3648, 4327, 5104, 6028, 7084, 8330, 9756, 11430, 13340, 15574, 18122, 21086, 24464, 28378, 32832, 37977, 43823

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,3

COMMENTS

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

LINKS

Table of n, a(n) for n=0..49.

Michael Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

FORMULA

Euler transform of period 32 sequence [ 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, ...].

- a(n) = A029838(4*n + 2).

a(n) ~ sqrt(2*(1+sqrt(2))) * exp(Pi*sqrt(n/2)) / (16*n^(3/4)). - Vaclav Kotesovec, Nov 07 2015

EXAMPLE

G.f. = 1 + x + 2*x^2 + 3*x^3 + 5*x^4 + 6*x^5 + 9*x^6 + 12*x^7 + 17*x^8 + ...

G.f. = q^15 + q^47 + 2*q^79 + 3*q^111 + 5*q^143 + 6*q^175 + 9*q^207 + ...

MATHEMATICA

a[ n_] := SeriesCoefficient[ Product[ (1 - x^k)^-{ 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0}[[Mod[k, 32, 1]]], {k, n}], {x, 0, n}];

PROG

(PARI) {a(n) = if( n<0, 0, polcoeff( prod(k=1, n, (1 - x^k + x * O(x^n))^-[ 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1][k%32 + 1]), n))};

CROSSREFS

Cf. A029838.

Sequence in context: A329165 A292444 A035948 * A244747 A241742 A212584

Adjacent sequences: A258936 A258937 A258938 * A258940 A258941 A258942

KEYWORD

nonn

AUTHOR

Michael Somos, Nov 07 2015

STATUS

approved