OFFSET
0,6
COMMENTS
If all subsets are allowed instead of just pairs (chords), we get A324173. The rightmost column is A000108 (see Riordan). - Gus Wiseman, Feb 27 2019
LINKS
P. Flajolet and M. Noy, Analytic Combinatorics of Chord Diagrams, in: Formal power series and algebraic combinatorics (FPSAC '00) Moscow, 2000, p 191-201, eq (2)
J. Riordan, The distribution of crossings of chords joining pairs of 2n points on a circle, Math. Comp., 29 (1975), 215-222.
J. Riordan, The distribution of crossings of chords joining pairs of 2n points on a circle, Math. Comp., 29 (1975), 215-222. [Annotated scanned copy]
EXAMPLE
From Gus Wiseman, Feb 27 2019: (Start)
Triangle begins:
1
0 1
0 1 2
0 4 6 5
0 27 36 28 14
0 248 310 225 120 42
0 2830 3396 2332 1210 495 132
0 38232 44604 29302 14560 6006 2002 429
0 593859 678696 430200 204540 81900 28392 8008 1430
Row n = 3 counts the following chord diagrams (see link for pictures):
{{1,3},{2,5},{4,6}} {{1,2},{3,5},{4,6}} {{1,2},{3,4},{5,6}}
{{1,4},{2,5},{3,6}} {{1,3},{2,4},{5,6}} {{1,2},{3,6},{4,5}}
{{1,4},{2,6},{3,5}} {{1,3},{2,6},{4,5}} {{1,4},{2,3},{5,6}}
{{1,5},{2,4},{3,6}} {{1,5},{2,3},{4,6}} {{1,6},{2,3},{4,5}}
{{1,5},{2,6},{3,4}} {{1,6},{2,5},{3,4}}
{{1,6},{2,4},{3,5}}
(End)
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
R. J. Mathar, Dec 06 2018
EXTENSIONS
Offset changed to 0 by Gus Wiseman, Feb 27 2019
STATUS
approved