OFFSET
0,3
FORMULA
PROG
(PARI) {a(n)=local(A=1+x+x*O(x^n)); for(i=0, n+2, B=subst(A^2, x, x^2); A=(A+B*(1-x-x^2)/(1-x-x^3+x*O(x^n))^2)/2); round(polcoeff(A+x*O(x^n), n))}
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, Jul 26 2004
STATUS
approved