Number of centered 6-valent trees with n nodes.

Terms

a(0) =0a(1) =1a(2) =0a(3) =1a(4) =1a(5) =2a(6) =3a(7) =7a(8) =11a(9) =26a(10) =52a(11) =120a(12) =266a(13) =640a(14) =1509a(15) =3702a(16) =9090a(17) =22781a(18) =57452a(19) =146783a(20) =377357a(21) =978342a(22) =2550611a(23) =6690242a(24) =17633855a(25) =46705333a(26) =124227015a(27) =331757697a(28) =889207207a(29) =2391478247