Number of oriented trees with n nodes.

Terms

a(0) =1a(1) =1a(2) =3a(3) =8a(4) =27a(5) =91a(6) =350a(7) =1376a(8) =5743a(9) =24635a(10) =108968a(11) =492180a(12) =2266502a(13) =10598452a(14) =50235931a(15) =240872654a(16) =1166732814a(17) =5702001435a(18) =28088787314a(19) =139354922608a(20) =695808554300