Number of alpha-labelings of trees on n vertices.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =18a(6) =46a(7) =132a(8) =418a(9) =1456a(10) =5510a(11) =22584a(12) =99696a(13) =472182a(14) =2387204a(15) =12837652a(16) =73141564a(17) =440211138a(18) =2789982898a(19) =18576745544