OFFSET
0,2
FORMULA
Euler transform of period 6 sequence [-3, -1, -4, -1, -3, -3, ...].
G.f.: Product_{k>=1} (1 - x^(2*k)) * (1 - x^(3*k)) * (1 - x^(6*k)) / (1 - x^k)^3.
A329955(3*n + 1) = -a(n).
EXAMPLE
G.f. = 1 - 3*x + 2*x^2 - 2*x^3 + 8*x^4 - 7*x^5 + 2*x^6 - 4*x^7 + ...
G.f. = q - 3*q^4 + 2*q^7 - 2*q^10 + 8*q^13 - 7*q^16 + 2*q^19 - 4*q^22 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ QPochhammer[ x]^3 QPochhammer[ x^3] QPochhammer[ x^6] / QPochhammer[ x^2]^2, {x, 0, n}];
PROG
(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x + A)^3 * eta(x^3 + A) * eta(x^6 + A) / eta(x^2 + A)^2, n))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Nov 29 2019
STATUS
approved