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A153729 Expansion of q^(-1/3) * (eta(q)^8 + 32 * eta(q^4)^8) in powers of q. 2
1, 24, 20, 0, -70, -192, 56, 0, -125, 480, 308, 0, 110, 0, -520, 0, 57, -1680, 0, 0, 182, 1536, -880, 0, 1190, 1344, 884, 0, 0, 0, -1400, 0, -1330, -3000, 1820, 0, -646, -3840, 0, 0, -1331, 7392, 380, 0, 1120, 0, 2576, 0, 0, 2640, 1748, 0, -3850, 0, -3400, 0, 2703, -12480, -2500, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

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

FORMULA

G.f. is a period 1 Fourier series which satisfies f(-1 / (36 t)) = 2592 (t / i)^4 g(t) where q = exp(2 Pi i t) and g() is g.f. for A153728.

a(4*n + 3) = 0.

a(n) = b(3*n + 1) where b(n) is multiplicative and b(3^e) = 0^e, b(2^e) = (-3/2) * (1+(-1)^e) * (-8)^(e/2), b(p^e) = (1/2) * (1+(-1)^e) * (-p^3) ^ (e/2) if p == 2 (mod 3), b(p^e) = b(p) * b(p^(e-1)) - p^3 * b(p^(e-2)) if p == 1 (mod 3) where b(p) = x * (x^2 -3*p), 4*p = x^2 + 3*y^2, |x|<|y| and x == 2 (mod 3). - Michael Somos, Mar 01 2011

EXAMPLE

q + 24*q^4 + 20*q^7 - 70*q^13 - 192*q^16 + 56*q^19 - 125*q^25 + ...

MATHEMATICA

QP = QPochhammer; s=QP[q]^8+32*q*QP[q^4]^8 + O[q]^60; CoefficientList[s, q] (* Jean-Fran├žois Alcover, Nov 25 2015, adapted from PARI *)

PROG

(PARI) {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x + A)^8 + 32 * x * eta(x^4 + A)^8, n))}

(PARI) {a(n) = local(A, p, e, x, y, a0, a1); if( n<0, 0, n = 3*n + 1; A = factor( n); prod( k=1, matsize(A)[1], if( p = A[k, 1], e = A[k, 2]; if( p==3, 0, if( p==2, -3 * ((e+1)%2) * (-8)^(e\2), if( p%3==2, if(e%2, 0, (-p^3) ^ (e/2)), forstep( y = sqrtint(4*p\3), sqrtint(p\3), -1, if( issquare( 4*p - 3*y^2, &x), if( x%3!=2, x = -x); break)); a0 = 1; a1 = y = x * (x^2 - 3*p); for( i=2, e, x = y*a1 - p^3*a0; a0 = a1; a1 = x); a1))))))} /* Michael Somos, Mar 01 2011 */

CROSSREFS

A000731(2*n) = A153728(n) = a(2*n). 24 * A000731(n) = a(4*n + 1).

Sequence in context: A284874 A216841 A293782 * A128560 A230340 A292102

Adjacent sequences:  A153726 A153727 A153728 * A153730 A153731 A153732

KEYWORD

sign

AUTHOR

Michael Somos, Dec 31 2008

STATUS

approved

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Last modified October 22 23:18 EDT 2018. Contains 316518 sequences. (Running on oeis4.)