77777...77777 (49-digits)

This number is a prime.

                       777777779 9999779666 9779686977 9666977999 9977777777

+

1111111122222112000211202021120002112222211111111 +

3333333300000330666033065603306660330000033333333 +

3333333377777337000733701073370007337777733333333 =

7777777799999779666977968697796669779999977777777 .

All four numbers are square-congruent primes. [Hartley]

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