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A143378 Expansion of q^(-1/24) * eta(q^2)^5 / (eta(q) * eta(q^4)^2) in powers of q. 5
1, 1, -3, -2, 2, -1, 0, 1, 2, 4, -2, 0, -1, -2, 2, -1, 0, -2, -2, -2, 0, 0, 1, 4, -2, 2, 1, 0, -2, 0, 4, 0, 2, 0, 0, 1, 0, -4, 0, -2, -3, 0, 2, 2, -4, 0, 0, 2, -2, 0, -2, -3, 2, 0, 2, 2, 0, 1, 4, 0, 0, 0, 2, 0, 0, -4, 0, 2, 0, 2, -1, 0, 0, 2, -2, 2, -2, -1, -2, -4, 0, 0, 0, -2, -2, 0, 0, 2, 2, -2, 2, 0, 1, 0, 0, -2, 0, 0, 0, -2, 5, 2, -4, 2, 0 (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

G. C. Greubel, Table of n, a(n) for n = 0..1000

M. Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

FORMULA

Expansion of phi(x) * f(-x) = phi(-x^2) * f(x) = chi(-x) * f(x)^2 = phi(-x^2)^2 / chi(-x) in powers of x where phi(), chi(), f() are Ramanujan theta functions.

Euler transform of period 4 sequence [ 1, -4, 1, -2, ...].

G.f. is a period 1 Fourier series which satisfies f(-1 / (576 t)) = 288^(1/2) (t/i) g(t) where q = exp(2 Pi i t) and g(t) is the g.f. for A143380.

G.f.: Product_{k>0} (1 - (-x)^k)^2 * (1 - x^(2*k-1)).

a(n) = A143377(4*n) = A143380(4*n).

EXAMPLE

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

G.f. = q + q^25 - 3*q^49 - 2*q^73 + 2*q^97 - q^121 + q^169 + 2*q^193 + ...

MATHEMATICA

a[ n_] := SeriesCoefficient[ QPochhammer[ x] EllipticTheta[ 3, 0, x], {x, 0, n}]; (* Michael Somos, Apr 07 2015 *)

a[ n_] := SeriesCoefficient[ QPochhammer[ -x] EllipticTheta[ 4, 0, x^2], {x, 0, n}]; (* Michael Somos, Apr 07 2015 *)

PROG

(PARI) {a(n) = my(A, p, e, x); if(n<0, 0, n *= 4; A = factor(6*n + 1); simplify( I^n * prod(k=1, matsize(A)[1], if(p = A[k, 1], e = A[k, 2]; if(p<5, 0, if(p%8==5 || p%24==23, !(e%2), if(p%8==3 || p%24==17, (-1)^(e\2) * !(e%2), for(i=1, sqrtint(p\6), if( issquare(p - 6*i^2, &x), break)); (e+1) * (kronecker(12, x) * I^((p-1) / 6))^e)))))))};

(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A)^5 / (eta(x + A) * eta(x^4 + A)^2), n))};

CROSSREFS

Cf. A143377, A143380.

Sequence in context: A155917 A291770 A287823 * A131961 A276426 A317872

Adjacent sequences:  A143375 A143376 A143377 * A143379 A143380 A143381

KEYWORD

sign

AUTHOR

Michael Somos, Aug 11 2008

STATUS

approved

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Last modified February 19 22:36 EST 2020. Contains 332061 sequences. (Running on oeis4.)