They are 'square' numbers. 6x6=36, 9x9=81 and 5x5=25. Some other square numbers are 64, 4, 9, 100 & 121
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
1; 4; 9; 16; 25; 36; 49; 64; 81; 100