The number of different permuations
for n numbers is:
n!n^22^nn^nn \log nHow many ways can you pick the first value in the permutation?
There are n ways to pick the first value. That
will leave n-1 values left.
This means there are n-1 ways to pick the
second value, which means that there were n(n-1)
ways to pick the first two values.
Keep picking remaining values in this way. Each time that
you pick a value from i choices, you are
multiplying the total number of ways to do things
by i.