which is the smallest number must be added to the number 23040 to make it a perfect square ?

If you calculate the square root of 23040  using calculator, we get 151.8.
and 151+1=152
and 152²=23104
23104-23040=64
So 64 must be added to 23040 to make it as a perfect square.
(23040+64=23104= 152²)