33333...33333 (81-digits)

This number is a prime.

                                                                3 3333333332
2222223325 5555233257 7752332577 7523325777 5233255555 2332222222 3333333333

      3 3 3 3 3 3 3 3 3
      3 2 2 2 2 2 2 2 3
      3 2 5 5 5 5 5 2 3
      3 2 5 7 7 7 5 2 3
      3 2 5 7 7 7 5 2 3
      3 2 5 7 7 7 5 2 3
      3 2 5 5 5 5 5 2 3
      3 2 2 2 2 2 2 2 3
      3 3 3 3 3 3 3 3 3

The smallest square-congruent prime of order 9 containing all four prime digits. [Rupinski]