G.f. satisfies A(x) = Product_{n>=0} (1 + (x*A(x)^2)^(3^n)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =23a(5) =97a(6) =424a(7) =1899a(8) =8706a(9) =40767a(10) =194277a(11) =938973a(12) =4590618a(13) =22660654a(14) =112787933a(15) =565421237a(16) =2852430654a(17) =14470063011a(18) =73768236466a(19) =377733782773