Why was this visual proof missed for 400 years? (Fermat's two square theorem)

Chit-chat on Lagrange's four-square theorem

Lagrange's Four-Square Theorem, PDF, Number Theory

Lagrange's four-square theorem, polynomials, diophantine equations, prime numbers

Lagrange's Four Squares Theorem

Pythagorean Theorem

Pythagorean Theorem

number theory - The Four Square Theorem and Integral Apollonian Circle Packings, is there any connection? - Mathematics Stack Exchange

SOLVED: In the following sequence of problems, we will start the proof of the Four-Square Theorem conjectured in the third century by Diophantus and proven by Lagrange in 1770 (since it took

Sum of Squares Function -- from Wolfram MathWorld

SOLUTION: Legendre's two, three and four square theorem (number theory) - Studypool