OFFSET
1,5
FORMULA
a(2n) = 0.
EXAMPLE
G.f.: A(x) = x - x^3 + 3*x^5 - 3*x^7 + 3*x^9 - 3*x^11 + x^13 - x^15 +...
PROG
(PARI) {a(n)=local(L4n=ceil(log(n+1)/log(4))); polcoeff(x*(1-x^2)*prod(k=1, L4n, 1 + x^(4^k)+x*O(x^n))^3, n)}
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, Dec 19 2010
STATUS
approved