Number of HHD-free graphs on n nodes.

Terms

a(0) =1a(1) =2a(2) =4a(3) =11a(4) =32a(5) =128a(6) =608a(7) =3689a(8) =27238a(9) =244922a(10) =2659678a(11) =35013106a(12) =562450090