G.f.: A(x) = x - A(-A(x)^2).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =16a(6) =32a(7) =65a(8) =138a(9) =316a(10) =792a(11) =2142a(12) =6052a(13) =17316a(14) =49160a(15) =137108a(16) =374632a(17) =1004668a(18) =2656872a(19) =6974510a(20) =18310220a(21) =48416528a(22) =129637152a(23) =352339898a(24) =971336204a(25) =2707410220a(26) =7596357720a(27) =21363062480a(28) =60019857952a(29) =168132717792