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单词 Combination Lock
释义

Combination Lock

Let a combination of buttons be a Sequence of disjoint nonempty Subsets of the Set . If the number of possible combinations is denoted , then satisfies the RecurrenceRelation

(1)

with . This can also be written
(2)

where the definition has been used. Furthermore,
(3)

where are Eulerian Numbers. In terms of the Stirling Numbers of the SecondKind ,
(4)

can also be given in closed form as
(5)

where is the Polylogarithm. The first few values of for , 2, ... are 1, 3, 13, 75, 541,4683, 47293, 545835, 7087261, 102247563, ... (Sloane's A000670).


The quantity

(6)

satisfies the inequality
(7)


References

Sloane, N. J. A. SequenceA000670/M2952in ``An On-Line Version of the Encyclopedia of Integer Sequences.''http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S.The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.

Velleman, D. J. and Call, G. S. ``Permutations and Combination Locks.'' Math. Mag. 68, 243-253, 1995.


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