G.f. satisfies A(x) = (1 + x/A(x))/(1 - x).

Terms

a(0) =1a(1) =2a(2) =0a(3) =4a(4) =-8a(5) =32a(6) =-112a(7) =432a(8) =-1696a(9) =6848a(10) =-28160a(11) =117632a(12) =-497664a(13) =2128128a(14) =-9183488a(15) =39940864a(16) =-174897664a(17) =770452480a(18) =-3411959808a(19) =15181264896a(20) =-67833868288a(21) =304256253952