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        A: Squares         C: Odd Squares
      _______                _______
     /       \              /       \
    |    1    |            |    1    |
     \_______/              \_______/
              \            /       \
               |          |    9    |
               |          \_______/
               |             |     |
               |             |     |
               |             |     |
               |             |     |
               |             |     |
               |             |     |
               |             |     |
               |             |     |
               |             |     |
              /             /       \
     \_______/             /         \
    |   16   |           |     25    |
     \_______/            \__________/
      |     |               |     |
      |     |               |     |
     /       \             /       \
  E = {0, 1, 2, ..., 19}