a(1) = 1 as the only way to tile a 1 X 1 square is with a square with dimensions 1 X 1.
a(2) = 1 as the only way to tile a 2 X 2 square is with a square with dimensions 2 X 2.
a(3) = 33. The possible tilings, excluding those equivalent by symmetry, are:
.
+---+---+---+ +---+---+---+ +---+---+---+ +---+---+---+ +---+---+---+
| | | | | | | | | | | | | |
+---+---+---+ +---+---+---+ +---+---+ + +---+---+---+ +---+---+---+
| | | | | | | | | | | | |
+ + + + + + + + + + + + +
| | | | | | | | | | | | |
+---+---+---+ +---+---+---+ +---+---+---+ +---+---+---+ +---+---+---+
.
The first tiling can occur in 4 different ways, the second in 8 different ways, the third in 8 different ways, the fourth in 4 different ways and the fifth in 8 different ways. There is also the single 3 X 3 rectangle. This gives 33 ways in total.
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