Number of ternary search trees on n keys.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =6a(5) =16a(6) =42a(7) =114a(8) =322a(9) =918a(10) =2673a(11) =7875a(12) =23457a(13) =70551a(14) =213846a(15) =652794a(16) =2004864a(17) =6190612a(18) =19207416a(19) =59850384a(20) =187217679a(21) =587689947a(22) =1850692506a(23) =5845013538a(24) =18509607753a(25) =58759391013a(26) =186958014766a(27) =596108115402