A060051 Number of n-block r-bicoverings.

1, 0, 0, 2, 79, 82117, 4936900199, 27555467226181396, 20554872166566046969648895, 2786548447182420815380482508924733911, 89607283195144164483079065133414172790220498449945, 864608448649084311874549352448884076627916391005243593208944730790

Offset

0,4

Comments

A bicovering is an r-bicovering if the intersection of every two blocks contains at most one 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..30

Formula

E.g.f. for number of n-block r-bicoverings of a k-set is exp(-x-1/2*x^2*y)*Sum_{i=0..inf} (1+y)^binomial(i, 2)*x^i/i!.

Example

There are 2 3-block r-bicoverings: {{1},{2},{1,2}} and {{1,2},{1,3},{2,3}}.

Crossrefs

Column sums of A060052.

Cf. A002718, A060053, A060069, A060070.

Sequence in context: A045484 A113152 A265585 * A100421 A319438 A371151

Adjacent sequences: A060048 A060049 A060050 * A060052 A060053 A060054

Keyword

easy,nonn

Author

Vladeta Jovovic, Feb 15 2001

Extensions

Terms a(11) and beyond from Andrew Howroyd, Jan 30 2020

Status

approved