The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A151880 Triangle: R*(n,k) (n>=2, k from 2 to n-1 or to 2 if n = 2), where R*(n,k) = number of trees with n nodes and k unlabeled end-nodes. 2
 1, 1, 1, 1, 1, 2, 3, 1, 3, 9, 12, 1, 4, 18, 52, 60, 1, 5, 30, 136, 360, 360 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,6 COMMENTS All nodes are labeled except for the end-nodes. LINKS Table of n, a(n) for n=0..21. F. Harary, A. Mowshowitz and J. Riordan, Labeled trees with unlabeled end-points, J. Combin. Theory, 6 (1969), 60-64. FORMULA There is an explicit formula in terms of Stirling numbers of the second kind. EXAMPLE Triangle (in fact the columns in the original have been reversed and the triangle transposed): (n=2) 1 (n=3) 1 (n=4) 1 1 (n=5) 1 2 3 (n=6) 1 3 9 12 (n=7) 1 4 18 52 60 (n=8) 1 5 30 136 360 360 CROSSREFS See A213262 for a better version with more terms and a program. Row sums give A001258. Sequence in context: A111589 A259760 A010027 * A108990 A145080 A065078 Adjacent sequences: A151877 A151878 A151879 * A151881 A151882 A151883 KEYWORD nonn,tabf AUTHOR N. J. A. Sloane, Jul 21 2009 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 25 11:18 EDT 2024. Contains 374588 sequences. (Running on oeis4.)