G.f. satisfies A(x) = 1 + 2*x + 2*x^2*A(x)^2.

Terms

a(0) =1a(1) =2a(2) =2a(3) =8a(4) =16a(5) =48a(6) =136a(7) =384a(8) =1184a(9) =3520a(10) =10944a(11) =34048a(12) =107008a(13) =340480a(14) =1087104a(15) =3502080a(16) =11333120a(17) =36867072a(18) =120491008a(19) =395276288a(20) =1301700608a(21) =4300414976a(22) =14250496000a(23) =47353233408a(24) =157747462144a(25) =526740717568