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What is the next number in this sequence: ...1, 8, 27, 64...

What is the next number in this sequence: ...1, 2, 3, 5...

What is the next number in this sequence: ...256, 16, 4...

If you need to put a fence around the outside of your circular yard, and the distance from one end to the other is 81 feet, how many feet will you need to surround your yard. Use 3.14 for π