OFFSET
1,2
FORMULA
G.f. satisfies: A( x*(1 - A(x))/(1 + A(x)) ) = x.
EXAMPLE
A(x) = x + 2*x^2 + 10*x^3 + 74*x^4 + 682*x^5 + 7274*x^6 + 86386*x^7 +...
A(A(x)) = x + 4*x^2 + 28*x^3 + 256*x^4 + 2752*x^5 + 33124*x^6 + 434524*x^7 +...
The series reversion of A(x) equals:
x*(1-A(x))/(1+A(x)) = x - 2*x^2 - 2*x^3 - 14*x^4 - 110*x^5 - 1058*x^6 -...
PROG
(PARI) {a(n)=local(A=x+x^2); if(n<1, 0, for(i=1, n, A=serreverse(x*((1-A)/(1+A+x*O(x^n))))); polcoeff(A, n))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jun 11 2008
STATUS
approved