G.f. A(x) satisfies A(A(A(A(x)))) = x + 4*x^2 + 16*x^3.

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =-15a(5) =81a(6) =-159a(7) =-1695a(8) =19857a(9) =-77775a(10) =-372351a(11) =6628545a(12) =-24096975a(13) =-232640751a(14) =2756221601a(15) =2199811873a(16) =-210934282287a(17) =553408050417