OFFSET
1,2
COMMENTS
G.f. A(x) satisfies A(4*x^2) = A(x) + A(-x) = -4*A(x)*A(-x). Also A(4*x^2) = 4 * A(x)^2/(1 + 4*A(x)).
PROG
(PARI) a(n)=local(A, m); if(n<1, 0, A=x+O(x^2); m=1; while(m<=n, m*=2; A=subst(A, x, x^2); A=A/2+sqrt(A^2/4+A)); polcoeff(A, n)*4^(n-1))
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, Mar 20 2004
STATUS
approved