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

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =27a(5) =74a(6) =208a(7) =600a(8) =1762a(9) =5244a(10) =15788a(11) =48006a(12) =147199a(13) =454618a(14) =1412960a(15) =4416016a(16) =13869998a(17) =43756124a(18) =138587784a(19) =440523892a(20) =1404849486a(21) =4493472836a(22) =14411800352a(23) =46338611632a(24) =149338703380a(25) =482315951104