OFFSET
2,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 2..2500
FORMULA
Euler transform of period 5 sequence [-3, -3, -3, -3, -12, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (5 t)) = 5^(3/2) (t/i)^6 g(t) where q = exp(2 Pi i t) and g() is the g.f. for A227900.
G.f.: x^2 * Product_{k>0} (1 - x^k)^3 * (1 - x^(5*k))^9.
EXAMPLE
G.f. = q^2 - 3*q^3 + 5*q^5 - 9*q^7 + 20*q^8 - 45*q^10 + 36*q^12 - 18*q^13 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ q^2 QPochhammer[ q]^3 QPochhammer[ q^5]^9, {q, 0, n}];
PROG
(PARI) {a(n) = my(A); if( n<2, 0, n-=2; A = x * O(x^n); polcoeff( (eta(x + A) * eta(x^5 + A)^3)^3, n))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Oct 15 2013
STATUS
approved