From Mordell's identities one can conclude that there exists a solution for all "n" except possibly those that are 1, 121, 169, 289, 361, or 529 modulo 840.
Mordell navaja polinomske enakosti, ki dajo tričlene egipčanske ulomke za 4/"n", ko je "n" ≡ 2 (mod 3) (zgoraj), 3 (mod 4), 5 (mod 8), 2 ali 3 (mod 5) in 3, 5 ali 6 (mod 7).