Number of asymmetric rooted trees with a forbidden limb of length 3.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =4a(7) =8a(8) =15a(9) =30a(10) =60a(11) =122a(12) =249a(13) =513a(14) =1061a(15) =2210a(16) =4620a(17) =9708a(18) =20472a(19) =43337a(20) =92023a(21) =196018a(22) =418653a(23) =896485a(24) =1924154a(25) =4139014a(26) =8921349a(27) =19266067a(28) =41679483a(29) =90318082