Sums of four squares — AnhThu Nguyen

LAGRANGE'S FOUR SQUARE THEOREM Theorems, Lagrange theorem, Number theory

Jacobi's four-square theorem - Wikipedia

Lagrange's four-square theorem - Wikiwand

Lagrange's Four-Square Theorem -- from Wolfram MathWorld

PDF] New parametrization of $A^2+B^2+C^2=3D^2$ and Lagrange's four-square theorem

Lagrange's Four Squares Theorem

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

PDF) Sums of four squares and Waring's Problem

Euler's four-square identity - Wikipedia

An Independent Quaternion Proof of Jacobi's Four Square Theorem