The phalanx problem in the third grade of primary school
The outermost square has 80 ÷ 4+ 1 = 2 1 (person) on each side.
It can also be understood as: if the four corners are removed first, there are still 80-4 = 76 people, so there are still 76 ÷ 4 = 19 people on each side, plus 2 people in each corner, which is 2 1 person.