457

This number is a prime.

If the symbols of Z340 are translated to a numeric form, where each unique symbol is assigned a unique number, then the sum of only one row (the 18th) is prime, i.e., 19 + 19 + 33 + 26 + 56 + 40 + 26 + 36 + 9 + 23 + 42 + 1 + 14 + 54 + 21 + 33 + 5 = 457. [Honaker]