Every Prime of the form is a sum of two Square Numbers in one unique way (up to the order of Summands). The theorem was stated by Fermat , but the first published proof was by Euler.

**References**

Hardy, G. H. and Wright, E. M. ``Some Notation.'' Th. 251 in
*An Introduction to the Theory of Numbers, 5th ed.* Oxford, England: Clarendon Press, 1979.

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1999-05-26