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A283826 Irregular triangle read by rows: T(n,k) = number of trees on n nodes with radius k, n>=1, 1 <= k <= floor(n/2). 3
0, 1, 1, 1, 1, 1, 2, 1, 4, 1, 1, 7, 3, 1, 11, 10, 1, 1, 17, 25, 4, 1, 25, 61, 18, 1, 1, 36, 132, 61, 5, 1, 50, 277, 194, 28, 1, 1, 70, 554, 553, 117, 6, 1, 94, 1077, 1495, 451, 40, 1, 1, 127, 2034, 3823, 1552, 197, 7, 1, 168, 3770, 9427, 5020, 879, 54, 1, 1, 222, 6853, 22466, 15289, 3485, 305, 8, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,7
COMMENTS
The radius of a tree is the maximal distance of a node from the center.
LINKS
Peter Steinbach, Field Guide to Simple Graphs, Volume 3, Part 8 (For Volumes 1, 2, 3, 4 of this book see A000088, A008406, A000055, A000664, respectively.)
FORMULA
T(n,k) = A034853(n,2k-1) + A034853(n,2k). - R. J. Mathar, Apr 03 2017
EXAMPLE
Triangle begins:
0,
1,
1,
1, 1,
1, 2,
1, 4, 1,
1, 7, 3,
1, 11, 10, 1,
1, 17, 25, 4,
1, 25, 61, 18, 1,
1, 36, 132, 61, 5,
1, 50, 277, 194, 28, 1,
...
CROSSREFS
Cf. A283827.
See also A000676, A000677, A027416, A102911, A004250 (column 2?), A000055 (row sums).
Sequence in context: A191525 A066633 A238415 * A088443 A117352 A137710
KEYWORD
nonn,tabf
AUTHOR
N. J. A. Sloane, Mar 19 2017
STATUS
approved

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Last modified March 28 04:58 EDT 2024. Contains 371235 sequences. (Running on oeis4.)