Catafusenes (see reference for precise definition).

Terms

a(0) =1a(1) =3a(2) =12a(3) =49a(4) =204a(5) =864a(6) =3714a(7) =16170a(8) =71178a(9) =316303a(10) =1417248a(11) =6396273a(12) =29051856a(13) =132700725a(14) =609200640a(15) =2809373915a(16) =13008512040a(17) =60457182345a(18) =281919911460