Forbidden numbers: Difference between revisions
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slight clarification
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Others require at least three squares. <code>'''6 == 2<sup>2</sup> + 1<sup>2</sup> + 1<sup>2</sup>'''</code>
Finally, some, (the focus of this task) require the sum at least four squares. <code>'''7 == 2<sup>2</sup> + 1<sup>2</sup> + 1<sup>2</sup> + 1<sup>2</sup>'''</code>. There is no way to reach 7
These numbers show up in crystallography; x-ray diffraction patterns of cubic crystals depend on a length squared plus a width squared plus a height squared. Some configurations that require at least four squares are impossible to index and are colloquially known as '''forbidden numbers'''.
Note that some numbers ''can'' be made from the sum of four squares: <code>'''16 == 2<sup>2</sup> + 2<sup>2</sup> + 2<sup>2</sup> + 2<sup>2</sup>'''</code>, but since it can also be formed from
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