The rules of 100, 81, 49, 36, (), 16, () are as follows

The rules of 100, 81, 49, 36, (), 16, () are as follows

25 and 9, respectively
100 is the square of 10
81 is the square of nine
64 is the square of 8
49 is the square of seven
36 is the square of 6
25 is the square of 5
So, is your original question wrong? It's missing a 64