155244

First, we need to establish what the pattern is. Let's try the number 3. We can see that 4^2=16 and that 2^2=4. The difference is 12, four times the number 3. This was the same trend with several numbers. Our conjecture is that the difference between the two squares is equal to x, the middle number x4.
Now, let's move to the algebraic part:
(x+1)(x+1)=x^2+2x+1
(x-1)(x-1) =x^2-2x+1
Therefore
(x^2+2x+1)-(x^2-2x+1)=?
This equals 4x thereby proving our conjecture.

Using the number 5, we can see that it works with te five times table (And any times table):
(25+10+1) - (25-10+1) = 20
36 16