Number of, not necessarily connected, regular simple graphs on n vertices with girth at least 6.

Terms

a(0) =1a(1) =1a(2) =2a(3) =1a(4) =2a(5) =1a(6) =3a(7) =2a(8) =3a(9) =2a(10) =3a(11) =2a(12) =4a(13) =3a(14) =6a(15) =4a(16) =7a(17) =5a(18) =13a(19) =7a(20) =42a(21) =10a(22) =398a(23) =13a(24) =7592a(25) =18a(26) =181251a(27) =25a(28) =4624534a(29) =33