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A060051 Number of n-block r-bicoverings. 21
1, 0, 0, 2, 79, 82117, 4936900199, 27555467226181396, 20554872166566046969648895, 2786548447182420815380482508924733911, 89607283195144164483079065133414172790220498449945 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=0..10.

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

Cf. A060052, A060053, A002718, A059443, A003462, A059945-A059951.

Sequence in context: A045484 A113152 A265585 * A100421 A319438 A195000

Adjacent sequences:  A060048 A060049 A060050 * A060052 A060053 A060054

KEYWORD

easy,nonn

AUTHOR

Vladeta Jovovic, Feb 15 2001

STATUS

approved

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Last modified March 20 15:43 EDT 2019. Contains 321345 sequences. (Running on oeis4.)