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A057270
Triangle T(n,k) of number of unilaterally connected digraphs on n unlabeled nodes with k arcs, k=0..n*(n-1).
7
1, 0, 1, 1, 0, 0, 1, 4, 4, 1, 1, 0, 0, 0, 1, 10, 30, 45, 38, 27, 13, 5, 1, 1, 0, 0, 0, 0, 1, 20, 136, 462, 972, 1412, 1639, 1485, 1152, 707, 379, 154, 61, 16, 5, 1, 1, 0, 0, 0, 0, 0, 1, 35, 437, 2833, 11325, 31615, 67207, 115344, 165762, 204723, 219866, 206986, 170920, 124088, 78809, 43860, 21209, 8951, 3242, 1043, 288, 76, 17, 5, 1, 1
OFFSET
1,8
REFERENCES
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973.
LINKS
R. W. Robinson, Counting strong digraphs (research announcement), J. Graph Theory 1, 1977, pp. 189-190.
EXAMPLE
[1],[0,1,1],[0,0,1,4,4,1,1],[0,0,0,1,10,30,45,38,27,13,5,1,1],...; Number of unilaterally connected digraphs on 4 unlabeled nodes is 171=1+10+30+45+38+27+13+5+1+1.
CROSSREFS
Row sums give A003088. Cf. A057271-A057279.
Sequence in context: A309748 A180401 A354043 * A057278 A010303 A046553
KEYWORD
nonn,tabf
AUTHOR
Vladeta Jovovic, Goran Kilibarda, Aug 23 2000
EXTENSIONS
More terms from Sean A. Irvine, May 27 2022
STATUS
approved