33333...33333 (289-digits)

This number is a prime.

                                                                   333333333
3333333331 1111111111 1111331333 3333333333 1331311111 1111113133 1313333333
3313133131 3111111131 3133131313 3333131313 3131313111 3131313313 1313131313
1313313131 3111313131 3313131333 3313131331 3131111111 3131331313 3333333313
1331311111 1111113133 1333333333 3333133111 1111111111 1133333333 3333333333

+

3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
3 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3
3 1 3 3 3 3 3 3 3 3 3 3 3 3 3 1 3
3 1 3 1 1 1 1 1 1 1 1 1 1 1 3 1 3
3 1 3 1 3 3 3 3 3 3 3 3 3 1 3 1 3
3 1 3 1 3 1 1 1 1 1 1 1 3 1 3 1 3
3 1 3 1 3 1 3 3 3 3 3 1 3 1 3 1 3 
3 1 3 1 3 1 3 1 1 1 3 1 3 1 3 1 3
3 1 3 1 3 1 3 1 3 1 3 1 3 1 3 1 3
3 1 3 1 3 1 3 1 1 1 3 1 3 1 3 1 3
3 1 3 1 3 1 3 3 3 3 3 1 3 1 3 1 3
3 1 3 1 3 1 1 1 1 1 1 1 3 1 3 1 3
3 1 3 1 3 3 3 3 3 3 3 3 3 1 3 1 3
3 1 3 1 1 1 1 1 1 1 1 1 1 1 3 1 3
3 1 3 3 3 3 3 3 3 3 3 3 3 3 3 1 3
3 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

A square-congruent prime of order 17 that contains only two digits, and for which adjacent bands contain different digits. Is this the largest possible? [Hartley]

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