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

Terms

a(0) =1a(1) =2a(2) =3a(3) =12a(4) =26a(5) =125a(6) =317a(7) =1642a(8) =4492a(9) =24188a(10) =69174a(11) =381613a(12) =1123923a(13) =6304781a(14) =18962485a(15) =107682542a(16) =329007674a(17) =1885923378a(18) =5833166568a(19) =33685017384a(20) =105214504816a(21) =611241171298