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A054547
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Triangular array giving number of labeled digraphs on n unisolated nodes and k=0..n*(n-1) arcs.
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5
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0, 0, 2, 1, 0, 0, 12, 20, 15, 6, 1, 0, 0, 12, 140, 435, 768, 920, 792, 495, 220, 66, 12, 1, 0, 0, 0, 240, 2520, 11604, 34150, 73560, 123495, 166860, 184426, 167900, 125965, 77520, 38760, 15504, 4845, 1140, 190, 20, 1
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OFFSET
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1,3
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LINKS
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FORMULA
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T(n, k) = Sum_{i=0..n} (-1)^(n-i)*binomial(n, i)*binomial(i*(i-1), k).
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EXAMPLE
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Triangle T(n,k) begins:
[0],
[0,2,1],
[0,0,12,20,15,6,1],
[0,0,12,140,435,768,920,792,495,220,66,12,1],
...
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PROG
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(PARI) row(n) = {Vecrev(sum(i=0, n, (-1)^(n-i)*binomial(n, i)*(1 + 'y)^(i*(i-1))), n*(n-1)+1)}
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CROSSREFS
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KEYWORD
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easy,nonn,tabf
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AUTHOR
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STATUS
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approved
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