Question 215180
How many permutations are there of 1,2,...,2n have 
every even number in an even-numbered position?
<pre>
There are {{{n}}} even integers and {{{n}}} odd integers.

There are {{{n!}}} ways to place the even integers.
For every one of those ways, there are {{{n!}}} ways 
to place the odd integers.

That's  {{{n!*n!=n!^2}}}

Edwin