Jacobi's four-square theorem

Chit-chat on Lagrange's four-square theorem

Sum of four Squares

Table 1 from Extended Lagrange's four-square theorem

数论代考, 四平方和定理The four square theorem 代写

Table 3 from Extended Lagrange's four-square theorem

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

Lagrange's Four-Square Theorem by Julian TSE

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

Proving the Pythagorean Theorem. Some algebraic and geometric proofs of…, by Michele Diodati, Not Zero

Euler's four-square identity - Wikipedia