OFFSET
0,4
FORMULA
G.f. satisfies: A(x)^2 = x*A( A(x)^2/x )/(1+x).
G.f. satisfies: A(x) = x + x*Series_Reversion( A(x)^2/x ). - Paul D. Hanna, Mar 15 2010
PROG
(PARI) {a(n)=local(A, B, F); if(n<1, 0, F=x+2*x^2+x*O(x^n); A=F; for(j=0, n, for(i=0, j, B=serreverse(A); A=(A+subst(B, x, A*(1+x)^2))/2); A=round(A)); polcoeff(sqrt(x*A), n, x))}
(PARI) {a(n)=local(A=1+x+x*O(x^n)); for(i=1, n, A=1+serreverse(x*subst(A^2, x, x+x*O(x^n)))); polcoeff(x*A, n)} \\ Paul D. Hanna, Mar 15 2010
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, May 12 2005
STATUS
approved