44445...77777 (39-digits)

This number is a prime.

                                  444455555 6666668888 8888999999 9997777777

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The smallest prime concatenated from the six larger rep-digit numbers, each of them formed by using d times the digit d, i.e., 4444, 55555, 666666, 7777777, 88888888, 999999999. [Loungrides]