The number of 4-regular plane graphs with n vertices with all faces 3-gons or 4-gons.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =0a(6) =1a(7) =1a(8) =2a(9) =1a(10) =5a(11) =2a(12) =8a(13) =5a(14) =12a(15) =8a(16) =25a(17) =13a(18) =30a(19) =23a(20) =51a(21) =33a(22) =76a(23) =51a(24) =109a(25) =78a(26) =144a(27) =106a(28) =218a(29) =150