来自在线整数百科全书的问候语!http://oeis.org/ Search: id:a054581 Showing 1-1 of 1 %I A054581 %S A054581 1,1,1,2,5,12,39,136,529,2171,9368,41534,188942,874906,4115060, %T A054581 19602156,94419351,459183768,2252217207,11130545494,55382155396, %U A054581 277255622646,1395731021610,7061871805974,35896206800034,183241761631584 %N A054581 Number of unlabeled 2-trees with n nodes. %C A054581 A 2-tree is recursively defined as follows: K_2 is a 2-tree and any 2-tree on n+1 vertices is obtained by joining a vertex to a 2-clique in a 2-tree on n vertices. 545 81A036361给出了这个序列的标记版本,它有一个类似于Cayley的树数公式的简单公式.%%C A0545 81n,没有标记的3-Gang-2树具有n个3个GON。%D A0545 81- Miklos Bona,编辑,列举组合数学手册,CRC出版社,2015,第327页-328页。%的A0545 81- F. Harary和E. M. Palmer,图形枚举,学术出版社,NY,1973,P 76,T(x),(3.5.19)。2词树(一般是k-树)是需要的,因为它至少有两个常用的定义。2-树的规范,Adv.Appl。数学28(2)(2002)145-168,表1 .%%H A0545 81- Andrew Gainer Dewar,Gamma种与K-树的计数《组合数学》电子杂志,第19卷(2012),第45页。-从12月15日J.A.SLaNeNe],12月15日2012,%A0545 81G拉贝尔,C. Lamathe和P. Leroux,k-树2-树的标号和无标记计数,阿西夫:数学/ 0312424 [数学.CO],2003。与树相关的序列的索引条目%E A0545 81A(1)=A(2)=A(3)=1,因为:KY2,KY3是2和3节点上仅有的2棵树,在4个节点上,也有一个独特的例子,通过将三角形连接到KY3沿边缘(从而形成Ky4\E)。The two graphs on 5 nodes are obtained by joining a triangle to K_4\e, either along the shared edge or along one of the non-shared edges. %Y A054581 Cf. A036361. %Y A054581 Cf. A000272 (labeled trees), A036361 (labeled 2-trees), A036362 (labeled 3-trees), A036506 (labeled 4-trees), A000055 (unlabeled trees). %K A054581 nonn,nice %O A054581 1,4 %A A054581 _Vladeta Jovovic_, Apr 11 2000 %E A054581 Additional comments from _Gordon F. Royle_, Dec 02 2002 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE