99999...99999 (169-digits)

This number is a prime.

                                             999999999 9999933333 3333339933
3333333339 9337777777 3399337999 9973399337 9333973399 3379373973 3993379333
9733993379 9999733993 3777777733 9933333333 3339933333 3333339999 9999999999

The largest square-congruent prime that is 2-deletable, i.e., removing the outer two most shells yields another square-congruent prime. Note that this can be repeated until you are down to the center nut. [Patterson]