Symmetries in unrooted 3-trees on n+1 vertices.

Terms

a(0) =1a(1) =2a(2) =2a(3) =8a(4) =4a(5) =14a(6) =21a(7) =35a(8) =49a(9) =158a(10) =191a(11) =425a(12) =828a(13) =1864a(14) =3659a(15) =8324a(16) =17344a(17) =39601a(18) =87407a(19) =199984a(20) =453361a(21) =1053816a(22) =2426228a(23) =5672389a(24) =13270695a(25) =31277150a(26) =73874375a(27) =175419550a(28) =417535487a(29) =997758788