Number of disconnected regular simple graphs on n vertices with girth at least 4.

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =2a(5) =1a(6) =2a(7) =1a(8) =3a(9) =2a(10) =4a(11) =3a(12) =7a(13) =5a(14) =10a(15) =8a(16) =22a(17) =12a(18) =54a(19) =20a(20) =218a(21) =62a(22) =1436a(23) =1731a(24) =27810a(25) =197981a(26) =2613814a(27) =33117962a(28) =463707741a(29) =6709514340