Sets of sequences

[Berny]

David Wilson dice:

> How many sets of sequences are there that include the numbers 1 through 
> n once? For n = 5, we might have
> 
> {(3, 1, 5), (4 ,2)}  and  {(1), (2, 4), (5, 3)} as examples.

They should be n!*2^(n-1), since you can write a sequence of n numbers 
in n! ways and then you can group them in 2^(n-1) ways.

First few sequences:
n=1 -> 1 : {(1)}
n=2 -> 4 : {(1,2)},{(2,1)},{(1),(2)} and {(2),(1)}
n=3 -> 24

                Berny Boncompagni

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