A105344 Number of ways of placing n balls into n boxes and then into n containers.

1, 4, 12, 45

Offset

1,2

Links

Table of n, a(n) for n=1..4.

Example

a(2): We can have either 2 balls in a box and the other box empty, or a ball in each box. We may place both the boxes into one container, or one in each.
So we have [(2)()][], [(1)(1)][], [(2)][()] and [(1)][(1)], hence a(2)=4.
For a(3) we have: (0 is an empty box, / is a new container, - is an empty container)
300/-/-, 30/0/-, 3/00/-, 3/0/0
210/-/-, 21/0/-, 20/1/-, 2/10/-, 2/1/0
111/-/-, 11/1/-, 1/1/1
total 12

Crossrefs

Cf. A000041.

Sequence in context: A065143 A098543 A028407 * A074035 A149366 A370540

Adjacent sequences: A105341 A105342 A105343 * A105345 A105346 A105347

Keyword

nonn

Author

Jon Perry, Apr 30 2005

Status

approved