2015 NS 23

Here's what I tried:

8 has to be in the middle

We can put the first number in 2 places: at the end or at the front

 

Then we can put the second number in 2 places, then the third, then the fourth, ... all the way to the 6th number

 

The 7th number has to be in the remaining spot.

 

So, I got 2^6= 64. How do you do this?