31313...32323 (108-digits)

This number is a prime.

                                   31313131 3131313131 3131313131 3131313131
3131313123 2323232323 2323232323 2323232323 2323232323 2323232323 2323232323

+ Twenty-three 31's followed by thirty-one 23's is prime. [De Geest]

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