G.f. A(x) satisfies x = (1 + 4*A(x)) * A(A(x)).

Terms

a(0) =1a(1) =-2a(2) =8a(3) =-36a(4) =160a(5) =-656a(6) =2368a(7) =-7664a(8) =29440a(9) =-184896a(10) =1174272a(11) =-3395200a(12) =-21222400a(13) =178961920a(14) =1638189056a(15) =-27449296640a(16) =-28875071488