Number of unlabeled 6-trees on n nodes.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =1a(7) =1a(8) =2a(9) =5a(10) =15a(11) =64a(12) =342a(13) =2344a(14) =19090a(15) =179562a(16) =1878277a(17) =21365403a(18) =258965451a(19) =3294561195a(20) =43472906719a(21) =589744428065