Square numbers are whole integers that can be made my multiplying an integer by itself. This is, in effect, literally _squaring_ the number line.
Fun facts:
- any number can be expressed as the sum of no more than 4 square numbers
- square numbers follow the sum of odd numbers (1, 1+3, 1+3+5).
- This is true because it takes the next bigger odd number to create a new layer around a literal square
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