KnowraLagrange's four-square theoremLinked fromLinked fromThe 10 pages that link to Lagrange's four-square theorem, each with the reason it gives.All 10Broader topic 3Related 2Compared with 5Jacobi's four-square theoremCompared with: Lagrange proved existence; Jacobi sharpened it by counting every representation.Fermat polygonal number theoremCompared with: It is a related bounded-sum theorem, but uses squares rather than n-gonal numbers.Brahmagupta–Fibonacci identityCompared with: It concerns universal representation by four squares, not multiplicative closure of two-square forms.Legendre's three-square theoremCompared with: Unlike the three-square theorem, it has no excluded congruence classes.Lemoine's conjectureCompared with: It illustrates a representation claim that is proved for every eligible integer, unlike Lemoine's conjecture.