99997...79999 (121-digits)

This number is a prime.

                    9 9997997799 9999777999 9997777777 7779977770 7777997700
0077997701 0779977000 0779977770 7777997777 7777779999 9977799999 9779979999

The largest star-congruent prime with 17 rows (containing 121 digits):

                  9
                 9 9
                9 7 9
               9 7 7 9
      9 9 9 9 9 7 7 7 9 9 9 9 9
       9 7 7 7 7 7 7 7 7 7 7 9
        9 7 7 7 7 0 7 7 7 7 9
         9 7 7 0 0 0 0 7 7 9
          9 7 7 0 1 0 7 7 9
         9 7 7 0 0 0 0 7 7 9
        9 7 7 7 7 0 7 7 7 7 9
       9 7 7 7 7 7 7 7 7 7 7 9
      9 9 9 9 9 7 7 7 9 9 9 9 9
               9 7 7 9
                9 7 9
                 9 9
                  9