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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). 10
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 (list; graph; refs; listen; history; text; internal format)
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..45.

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: A163353 A164612 A180401 * A057278 A010303 A046553

Adjacent sequences:  A057267 A057268 A057269 * A057271 A057272 A057273

KEYWORD

more,nonn,tabf

AUTHOR

Vladeta Jovovic, Goran Kilibarda, Aug 23 2000

STATUS

approved

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Last modified February 22 05:17 EST 2019. Contains 320385 sequences. (Running on oeis4.)