Number of disconnected 4-valent (or quartic) graphs with n nodes.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =0a(9) =0a(10) =1a(11) =1a(12) =3a(13) =8a(14) =25a(15) =88a(16) =378a(17) =2026a(18) =13351a(19) =104595a(20) =930586a(21) =9124662a(22) =96699987a(23) =1095469608a(24) =13175272208a(25) =167460699184