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A060069
Number of n-block T_0-tricoverings.
11
1, 0, 0, 0, 2, 82194, 9185157387760082, 5573096894405951375691132323893805593, 47933892393105239218152796441416602126447041437452022947424986090407628
OFFSET
0,5
COMMENTS
A covering of a set is a tricovering if every element of the set is covered by exactly three blocks of the covering; A covering of a set is a T_0-covering if for every two distinct elements of the set there exists a block of the covering containing one but not the other element.
REFERENCES
I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, John Wiley and Sons, N.Y., 1983.
LINKS
FORMULA
E.g.f. for n-block T_0-tricoverings of a k-set is exp(-x+1/2*x^2+1/3*x^3*y)*Sum_{i=0..inf} (1+y)^binomial(i, 3)*exp(-1/2*x^2*(1+y)^i)*x^i/i!.
CROSSREFS
Column sums of A059530.
Sequence in context: A071067 A321246 A371645 * A354177 A231612 A296104
KEYWORD
nonn
AUTHOR
Vladeta Jovovic, Feb 19 2001
STATUS
approved