Number of free trees of n vertices whose automorphisms are a 2-group.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =2a(6) =4a(7) =6a(8) =13a(9) =26a(10) =56a(11) =122a(12) =278a(13) =634a(14) =1494a(15) =3540a(16) =8542a(17) =20774a(18) =51116a(19) =126648a(20) =316452a(21) =795510a(22) =2012476a(23) =5117613a(24) =13079677a(25) =33576706a(26) =86555074a(27) =223965633a(28) =581573118a(29) =1515084771