55555...55557 (88-digits)

This number is a prime.

                                                         55555555 5555555555
5555555555 5555555555 5555555555 5555555555 5555555555 5555555555 5555555557

+ The largest near-repdigit prime p smaller than a googol found in the sequence 7, 57, 557, 5557, 55557, 555557, 5555557, etc. Curiously, p is also expressible as the sum of two squares. [Bajpai]

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