A057270 Triangle T(n,k) of number of unilaterally connected digraphs on n unlabeled nodes with k arcs, k=0..n*(n-1).

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

Table of n, a(n) for n=1..76.

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

Adjacent sequences: A057267 A057268 A057269 * A057271 A057272 A057273

Keyword

nonn,tabf

Author

Vladeta Jovovic, Goran Kilibarda, Aug 23 2000

Extensions

More terms from Sean A. Irvine, May 27 2022

Status

approved