In general, we can say that there are 2n non-perfect square numbers between the squares of the numbers n and (n + 1).
For example, consider,
n=4 and n+1=5
42=16 and 52=25
The non-square numbers between 16 and 25 are 17, 18, 19, 20, 21, 22, 23, 24. i.e., 8 numbers
Now, 8=2×4
⇒ There are 2n non-perfect square numbers between the squares of the numbers n and (n + 1).