G.f.=x+x^2+2*x^3+4*x^4+9*x^5+20*x^6+48*x^7+115*x^8+。。。
具有6个节点的a(6)=20树具有以下级别序列(根级别=0)和括号单词:
01: [ 0 1 2 3 4 5 ] (((((())))))
02: [ 0 1 2 3 4 4 ] ((((()()))))
03: [ 0 1 2 3 4 3 ] ((((())())))
04: [ 0 1 2 3 4 2 ] ((((()))()))
05: [ 0 1 2 3 4 1 ] ((((())))())
06: [ 0 1 2 3 3 3 ] (((()()())))
07: [ 0 1 2 3 3 2 ] (((()())()))
08: [ 0 1 2 3 3 1 ] (((()()))())
09: [ 0 1 2 3 2 3 ] (((())(())))
10: [ 0 1 2 3 2 2 ] (((())()()))
11: [ 0 1 2 3 2 1 ] (((())())())
12: [ 0 1 2 3 1 2 ] (((()))(()))
13: [ 0 1 2 3 1 1 ] (((()))()())
14: [ 0 1 2 2 2 2 ] ((()()()()))
15: [ 0 1 2 2 2 1 ] ((()()())())
16: [ 0 1 2 2 1 2 ] ((()())(()))
17: [ 0 1 2 2 1 1 ] ((()())()())
18: [ 0 1 2 1 2 1 ] ((())(())())
19: [ 0 1 2 1 1 1 ] ((())()()())
20: [ 0 1 1 1 1 1 ] (()()()()())
(结束)