Number of "nonlinear" trees on n nodes.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =4a(6) =16a(7) =51a(8) =158a(9) =463a(10) =1330a(11) =3742a(12) =10438a(13) =28877a(14) =79619a(15) =218997a(16) =602079a(17) =1655623a(18) =4557604a(19) =12564084a(20) =34697544a(21) =96006605a(22) =266185703a(23) =739530680a(24) =2058786037a(25) =5742859294a(26) =16050179897a(27) =44939957405a(28) =126052336580a(29) =354158412141