Sum of two squares theorem - Wikipedia

Sum of four Squares

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

Jacobi's four-square theorem - Wikipedia

PDF) Extended Lagrange's four-square theorem

Square Number Definition & Meaning

2023 Number Challenge: Find sum of four squares that is equal to 2023

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

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, Part-2, Sum of four squares

Waring's Problem -- from Wolfram MathWorld