(1) solid square: (number of people on each side of the outer layer) 2= total number of people.

(2) Hollow square:

(number of people on each side of the outermost layer) 2- (number of people on each side of the outermost layer -2× number of layers) 2= number of hollow squares.

Or:

(Number of people on each side of the outermost layer-number of layers) × number of layers× 4 = number of hollow squares.

Total number of people ÷4÷ layers+layers = number of people on each side of the outer layer.

For example, there is a three-story hollow square with 10 people on the outermost layer. How many people are there in the whole square?

Scheme 1 is regarded as a solid square, and the total number of people is:

10× 10= 100 (person)

Then calculate the square of the hollow part. From the outside to the inside, every time you enter a floor, if there are less than two people on each side, you will enter the fourth floor. The number of people on each side is:

10-2×3=4 (person)

Therefore, the number of squares in the hollow part is:

4×4= 16 (person)

So the number of people in this empty box is:

100- 16=84 (person)

Solution 2 directly applies the formula. According to the formula of the total number of hollow square:

(10-3)×3×4=84 (person)