Discrete quantum computation and Lagrange's four-square theorem

Sum of four Squares

Euler's four-square identity

Jacobi's four-square theorem - Wikipedia

PDF) A Simple Proof of Jacobi's Four-Square Theorem

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

FERMAT'S FOUR SQUARES THEOREM Several years ago, after

CodeChef - Lagrange's four-square theorem, also known as Bachet's conjecture, states that every natural number can be represented as the sum of four integer squares. This theorem was proven by Joseph Louis

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

Lagrange's Four-Square Theorem by Julian TSE

Waring's Problem -- from Wolfram MathWorld