Number of n-node 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) =7a(8) =14a(9) =28a(10) =61a(11) =131a(12) =297a(13) =678a(14) =1592a(15) =3770a(16) =9096a(17) =22121a(18) =54451a(19) =135021a(20) =337651a(21) =849698a(22) =2152048a(23) =5479408a(24) =14022947a(25) =36048514a(26) =93061268a(27) =241160180a(28) =627179689a(29) =1636448181