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Fermat's Theorem on Sums of Two Squares

Number Theory

Fermat's Theorem on Sums of Two Squares states that an odd prime number can be written as the sum of two perfect squares if and only if it leaves a remainder of one when divided by four. Attributed to Pierre de Fermat, it is a classical result of number theory that was later given a full proof by Leonhard Euler.

Facts
Statement
The theorem states that an odd prime p can be written as the sum of two integer squares if and only if p leaves remainder 1 when divided by 4. 1
Proof Year
1749 1
Fermat stated the claim without a published proof in a December 25, 1640 letter to Marin Mersenne. Euler gave the first proof, by infinite descent, communicated in an April 12, 1749 letter to Goldbach.
Classification
Statement Form
Existence Theorem 1
Statement Form
Characterization Theorem 1
Connections

In Branch

Named After

Pierre de Fermat, Mathematicians

Derived from the theorem's own name (unambiguous possessive-token match to exactly one live mathematician entity, w-bfill-g5-0924 browse backfill)

Posed By

Proved By

Sources
1. Fermat's Theorem on Sums of Two Squares (Wikipedia)
Wikimedia Foundation
  • Wikipedia, Fermat's theorem on sums of two squares, lead section
    In additive number theory, Fermat's theorem on sums of two squares states that an odd prime p can be expressed as:
  • Wikipedia, Fermat's theorem on sums of two squares, Euler's proof section
    Euler succeeded in proving Fermat's theorem on sums of two squares in 1749, when he was forty-two years old. He communicated this in a letter to Goldbach dated 12 April 1749.
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