Number of n-node trees with a forbidden limb of length 4.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =2a(6) =5a(7) =9a(8) =19a(9) =38a(10) =86a(11) =188a(12) =439a(13) =1026a(14) =2472a(15) =5997a(16) =14835a(17) =36964a(18) =93246a(19) =236922a(20) =607111a(21) =1565478a(22) =4062797a(23) =10599853a(24) =27797420a(25) =73224806a(26) =193709710a(27) =514406793a(28) =1370937140a(29) =3665714528