11111...11111 (289-digits)

This number is a prime.

                                                                   111111111
1111111112 2222222222 2222112333 3333333333 2112344444 4444443211 2348888888
8843211234 8999999984 3211234895 5555984321 1234895666 5984321123 4895676598
4321123489 5666598432 1123489555 5598432112 3489999999 8432112348 8888888843
2112344444 4444443211 2333333333 3333211222 2222222222 2211111111 1111111111

     1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
     1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1
     1 2 3 3 3 3 3 3 3 3 3 3 3 3 3 2 1
     1 2 3 4 4 4 4 4 4 4 4 4 4 4 3 2 1
     1 2 3 4 8 8 8 8 8 8 8 8 8 4 3 2 1
     1 2 3 4 8 9 9 9 9 9 9 9 8 4 3 2 1
     1 2 3 4 8 9 5 5 5 5 5 9 8 4 3 2 1 
     1 2 3 4 8 9 5 6 6 6 5 9 8 4 3 2 1 
     1 2 3 4 8 9 5 6 7 6 5 9 8 4 3 2 1
     1 2 3 4 8 9 5 6 6 6 5 9 8 4 3 2 1
     1 2 3 4 8 9 5 5 5 5 5 9 8 4 3 2 1
     1 2 3 4 8 9 9 9 9 9 9 9 8 4 3 2 1
     1 2 3 4 8 8 8 8 8 8 8 8 8 4 3 2 1
     1 2 3 4 4 4 4 4 4 4 4 4 4 4 3 2 1
     1 2 3 3 3 3 3 3 3 3 3 3 3 3 3 2 1
     1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1
     1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

The smallest square-congruent prime containing all non-zero digits. [Hartley]