4,4,4,5,5,5,6,6,7,8,8,8,9,10,10,10,10
It is the number 7.
A perfect square is a number that can be expressed as the product of two equal integers.
The only way to accurately calculate if a number is a perfect square is to find the factors. Before we go through the trouble of finding the factors, there is a quick trick you can use to help determine if you need even need to do the extra work.