Number of connected graphs with n vertices which have a planar square.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =6a(5) =6a(6) =14a(7) =25a(8) =60a(9) =124a(10) =302a(11) =696a(12) =1745a(13) =4300a(14) =11042a(15) =28362a(16) =74483a(17) =196539a(18) =525521a(19) =1413635a(20) =3835932a(21) =10468384