Sorry, this prob may have been posted before

The problem goes like this

for what integral value of n will the expression

2*n / (n-4) be a positive integer.

obviously the n must be greater than 4

and we can show that the expression is integer for
n = 5, 6, 8, 12

however, how do we prove that no n from 13 and onwards will give the expression an integral value?