Number of simple 4-regular 4-edge-connected but not 3-connected plane graphs on n nodes.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =1a(7) =1a(8) =6a(9) =16a(10) =59a(11) =188a(12) =685a(13) =2412a(14) =8825a(15) =32110a(16) =118505a(17) =437526a(18) =1624492a(19) =6043496a(20) =22553387a(21) =84345031a(22) =316183706a(23) =1187740914a(24) =4471145942a(25) =16864755973a(26) =63737132585a(27) =241337964503a(28) =915500561602