Triangle read by rows: labeled trees counted by improper edges.

Terms

a(0) =1a(1) =1a(2) =2a(3) =1a(4) =6a(5) =7a(6) =3a(7) =24a(8) =46a(9) =40a(10) =15a(11) =120a(12) =326a(13) =430a(14) =315a(15) =105a(16) =720a(17) =2556a(18) =4536a(19) =4900a(20) =3150a(21) =945a(22) =5040a(23) =22212a(24) =49644a(25) =70588a(26) =66150a(27) =38115a(28) =10395a(29) =40320