|
Search: id:A002989
|
|
|
| A002989 |
|
Number of n-node trees with a forbidden limb of length 3. (Formerly M1082)
|
|
+0 2
|
|
| 1, 1, 1, 1, 1, 2, 4, 7, 14, 28, 61, 131, 297, 678, 1592, 3770, 9096, 22121, 54451, 135021, 337651, 849698, 2152048, 5479408, 14022947, 36048514, 93061268, 241160180, 627179689, 1636448181, 4282964600, 11241488853, 29584389474
(list; graph; listen)
|
|
|
OFFSET
|
0,6
|
|
|
COMMENT
|
A tree with a forbidden limb of length k is a tree where the path from any leaf inward hits a branching node or another leaf within k steps.
|
|
REFERENCES
|
A. J. Schwenk, Almost all trees are cospectral, pp. 275-307 of F. Harary, editor, New Directions in the Theory of Graphs. Academic Press, NY, 1973.
|
|
LINKS
|
Index entries for sequences related to trees
|
|
FORMULA
|
G.f.: 1+B(x)+(B(x^2)-B(x)^2)/2 where B(x) is g.f. of A050321.
|
|
CROSSREFS
|
Cf. A002955, A002988-A002992, A052318-A052329.
Adjacent sequences: A002986 A002987 A002988 this_sequence A002990 A002991 A002992
Sequence in context: A119341 A119342 A119268 this_sequence A000671 A120262 A013326
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
njas
|
|
EXTENSIONS
|
More terms, formula and comments from Christian G. Bower (bowerc(AT)usa.net), Dec 15 1999.
|
|
|
Search completed in 0.002 seconds
|