12255...55221 (49-digits)

This number is a prime.

                       122555553 3366666677 7777767777 7776666663 3355555221

The smallest square-congruent prime of order 7 consisting of six positive digits d, i.e., (1, 2, 3, 5, 6, 7), 2*d times each of them and an extra digit in the middle. [Loungrides]