They are 'square' numbers. 6x6=36, 9x9=81 and 5x5=25. Some other square numbers are 64, 4, 9, 100 & 121
Square numbers less than 81 are the squares of integers from 0 to 8. They include 0, 1, 4, 9, 16, 25, 36, 49, 64, and 81. Therefore, the square numbers less than 81 are 0, 1, 4, 9, 16, 25, 36, 49, and 64.
25 36 49 64 81
4, 9, 16, 25, 36, 49, 64, 81
They are all perfect squares.
1, 4, 9, 16, 25, 36, 49, 64, 81, 100
0, 1, 4, 9, 16, 25, 36, 49, 64, 81
1, 4, 9, 16, 25, 36, 49, 64, 81, 100
1491625364964811001, 4, 9, 16, 25, 36, 49, 64, 81, and 100
1, 4, 9, 16, 25, 36, 49, 64, 81
1, 4, 9, 16, 25, 36, 49, 64, 81, 100
1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144
4,9,16,25,36,49,64,81,100,121