[seqfan] Magic squares of primes(?)

[Zak Seidov]

 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