Perfect Powers Square
In the following 2x2 grid,
8 4
1 6
there are 6 different perfect powers: 1, 4, 8, 16, 64, 81.

Fill a 3x3 grid with single digits to get the largest number of perfect
powers. Numbers are read up, down, left or right (not diagonally),
and are 1, 2 or 3 digits long.
 Repeat #1 with the restriction that all nine digits be unique.
Source: Original.
Solution
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