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A105344 Number of ways of placing n balls into n boxes and then into n containers. 0
1, 4, 12, 45 (list; graph; refs; listen; history; text; internal format)
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 A149367

Adjacent sequences:  A105341 A105342 A105343 * A105345 A105346 A105347

KEYWORD

nonn

AUTHOR

Jon Perry, Apr 30 2005

STATUS

approved

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Last modified December 16 04:05 EST 2019. Contains 330013 sequences. (Running on oeis4.)