[math-fun] Magic squares of primes(?)

Fill NxN square with decimal digits such that all rows/columns and 2 main diagonals read primes. Simple(st?) 3x3 case: 227 727 733 with 227,727,733,277,223,773,223 and 727 all primes. Cases with all primes distinct? Larger (largest?) cases? Old hat? zak