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A256505 Expansion of phi(x^3) * phi(-x^48) / chi(-x^16) in powers of x where phi(), chi() are Ramanujan theta functions. 2
1, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 1, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 2, 2, 0, 0, 0, 1, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 2, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 3, 0, 0, 2, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

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

M. Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

FORMULA

Expansion of q^(-2/3) * eta(q^6)^5 * eta(q^32) * eta(q^48)^2 / (eta(q^3)^2 * eta(q^12)^2 * eta(q^16) * eta(q^96)) in powers of q.

Euler transform of a period 96 sequence.

a(n) = A257403(3*n + 2) unless n == 5 (mod 8).

a(4*n + 1) = a(4*n + 2) = a(8*n + 7) = a(16*n + 4) = a(16*n + 8) = 0.

a(4*N) = A257399(n). a(8*n+3) = 2*A255318(n). a(16*n) = A257398(n). a(16*n+12) = 2*A255317(n).

EXAMPLE

G.f. = 1 + 2*x^3 + 2*x^12 + x^16 + 2*x^19 + 2*x^27 + 2*x^28 + x^32 + ...

G.f. = q^2 + 2*q^11 + 2*q^38 + q^50 + 2*q^59 + 2*q^83 + 2*q^86 + q^98 + ...

MATHEMATICA

a[ n_] := SeriesCoefficient[ EllipticTheta[ 3, 0, x^3] EllipticTheta[ 4, 0, x^48] QPochhammer[ -x^16, x^16], {x, 0, n}];

PROG

(PARI) {a(n) = my(A, p, e); if( n<0 || n%8 == 5, 0, A = factor(3*n + 2); prod( k=1, matsize(A)[1], [p, e] = A[k, ]; if( p<5, p+e==3, p%8 > 4, 1-e%2, e+1)))};

(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^6 + A)^5 * eta(x^32 + A) * eta(x^48 + A)^2 / (eta(x^3 + A)^2 * eta(x^12 + A)^2 * eta(x^16 + A) * eta(x^96 + A)), n))};

CROSSREFS

Cf. A255317, A255318, A257398, A257399, A257403.

Sequence in context: A084863 A233441 A255365 * A073346 A114099 A028613

Adjacent sequences:  A256502 A256503 A256504 * A256506 A256507 A256508

KEYWORD

nonn

AUTHOR

Michael Somos, Apr 22 2015

STATUS

approved

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Last modified December 12 15:11 EST 2019. Contains 329960 sequences. (Running on oeis4.)