Number of labeled acyclic digraphs with n nodes containing exactly n-1 points of in-degree zero.

Terms

a(0) =0a(1) =2a(2) =9a(3) =28a(4) =75a(5) =186a(6) =441a(7) =1016a(8) =2295a(9) =5110a(10) =11253a(11) =24564a(12) =53235a(13) =114674a(14) =245745a(15) =524272a(16) =1114095a(17) =2359278a(18) =4980717a(19) =10485740a(20) =22020075a(21) =46137322a(22) =96468969a(23) =201326568a(24) =419430375a(25) =872415206a(26) =1811939301a(27) =3758096356a(28) =7784628195a(29) =16106127330