f(x) = x + f(x^2 + x^3)

from numpy.polynomial.polynomial import *

z=Polynomial([0,1])

def Gn(n, G):
    if n == 0:
        return z
    else:
        return G(Gn(n-1,G))

def G(z):
    return z**2 + z**3

f = sum([Gn(n, G) for n in range(10)])
print f.coef[:22]
plot(f.coef[:22])