A060069 Number of n-block T_0-tricoverings.

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

Andrew Howroyd, Table of n, a(n) for n = 0..15

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.

Cf. A060051, A060053, A060070, A060486.

Sequence in context: A071067 A321246 A371645 * A354177 A231612 A296104

Adjacent sequences: A060066 A060067 A060068 * A060070 A060071 A060072

Keyword

nonn

Author

Vladeta Jovovic, Feb 19 2001

Status

approved