G.f. satisfies: A(x)^2 = A( x^2/(1 - 2*x - 4*x^2) ).

Terms

a(0) =1a(1) =1a(2) =4a(3) =10a(4) =34a(5) =106a(6) =361a(7) =1219a(8) =4252a(9) =14932a(10) =53263a(11) =191533a(12) =695233a(13) =2540617a(14) =9344050a(15) =34546672a(16) =128330533a(17) =478653973a(18) =1791816967a(19) =6729202603a(20) =25344884479a(21) =95707901503a(22) =362269464487