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A057278
Triangle T(n,k) of number of digraphs with a source and a sink on n unlabeled nodes and k arcs, k=0..n*(n-1).
9
1, 0, 1, 1, 0, 0, 1, 4, 4, 1, 1, 0, 0, 0, 1, 11, 31, 45, 38, 27, 13, 5, 1, 1, 0, 0, 0, 0, 1, 23, 152, 486, 992, 1419, 1641, 1485, 1152, 707, 379, 154, 61, 16, 5, 1, 1, 0, 0, 0, 0, 0, 1, 42, 517, 3194, 12174, 32860, 68423, 116168, 166164, 204867, 219906, 206993, 170922, 124088, 78809, 43860, 21209, 8951, 3242, 1043, 288, 76, 17, 5, 1, 1
OFFSET
1,8
REFERENCES
V. Jovovic, G. Kilibarda, Enumeration of labeled initially-finally connected digraphs, Scientific review, Serbian Scientific Society, 19-20 (1996), p. 246.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..2680 (rows 1..20)
EXAMPLE
Triangle begins:
[1],
[0,1,1],
[0,0,1,4,4,1,1],
[0,0,0,1,11,31,45,38,27,13,5,1,1],
...
The number of digraphs with a source and a sink on 3 unlabeled nodes is 11 = 1+4+4+1+1.
PROG
(PARI) \\ See PARI link in A350794 for program code.
{ my(A=A057278triang(5)); for(n=1, #A, print(A[n])) } \\ Andrew Howroyd, Jan 21 2022
CROSSREFS
Row sums give A049531.
Column sums give A350906.
The labeled version is A057271.
Sequence in context: A180401 A354043 A057270 * A010303 A046553 A046552
KEYWORD
nonn,tabf
AUTHOR
Vladeta Jovovic, Goran Kilibarda, Sep 14 2000
EXTENSIONS
Terms a(46) and beyond from Andrew Howroyd, Jan 21 2022
STATUS
approved