Number of quaternary rooted identity (distinct subtrees) trees with n nodes.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =6a(6) =12a(7) =25a(8) =52a(9) =113a(10) =247a(11) =548a(12) =1226a(13) =2770a(14) =6298a(15) =14419a(16) =33183a(17) =76760a(18) =178327a(19) =415960a(20) =973693a(21) =2286781a(22) =5386573a(23) =12723097a(24) =30127465a(25) =71506140a(26) =170081575a(27) =405359177a(28) =967899981a(29) =2315131955