Number of connected regular graphs with n nodes and girth at least 4.

Terms

a(0) =1a(1) =1a(2) =1a(3) =0a(4) =1a(5) =1a(6) =2a(7) =1a(8) =4a(9) =1a(10) =10a(11) =3a(12) =37a(13) =32a(14) =340a(15) =1608a(16) =18020a(17) =193907a(18) =2867725a(19) =32674058a(20) =1581632114a(21) =6705889824