D^3(1)=(12*x^2+56*x+52)/(x-1)^6。在x=0时计算得出a(4)=52。
a(3)=8:在3个顶点上的8个可能增加的平面树,其超度数k>=1的顶点有2种颜色,B或W,如下所示
.......................................................
.1B..1B段。.1瓦..1瓦。….1亿。……1瓦。…….1亿。……1W。...
.|...|...|...|...../.\....../..\....../..\....../..\...
.2B..2瓦。.2B..2瓦。..2...3....2....3....3....2....3....2..
.|...|...|...|.........................................
.3...3...3...3.........................................
G.f.=x+2*x^2+8*x^3+52*x^4+472*x^5+5504*x^6+78416*x^7+。..