A275517 Number of n-block bicoverings of an n-set.

1, 0, 0, 4, 39, 472, 7255, 131876, 2771685, 66253552, 1775801814, 52761229240, 1721387545471, 61187851111432, 2353835271333611, 97437447411025008, 4318780849687684325, 204079128112017902848, 10241833975586335217950, 544031400274026445420368

Offset

0,4

Links

Alois P. Heinz, Table of n, a(n) for n = 0..150

Formula

a(n) = n! * [(x*y)^n] 1/exp(x+x^2/2*(exp(y)-1)) * Sum_{j>=0} x^j/j! * exp(C(j,2)*y).

a(n) = A059443(n,n).

a(n)/n! ~ c * d^n / n, where d = 2.942382880944169398..., c = 0.1111860502273875... . - Vaclav Kotesovec, Aug 02 2016

Example

a(3) = 4: 1|123|23, 12|13|23, 12|123|3, 123|13|2.

Crossrefs

Main diagonal of A059443.

Sequence in context: A046449 A203211 A214823 * A300187 A068187 A307698

Adjacent sequences: A275514 A275515 A275516 * A275518 A275519 A275520

Keyword

nonn

Author

Alois P. Heinz, Jul 31 2016

Status

approved