10310...31313 (245-digits)

This number is a prime.

                                      10310 3103103103 1031031031 0310310310
3103131313 1313131313 1313131313 1313131313 1313131313 1313131313 1313131313
1313131313 1313131313 1313131313 1313131313 1313131313 1313131313 1313131313
1313131313 1313131313 1313131313 1313131313 1313131313 1313131313 1313131313

+ Thirteen 103's followed by one-hundred and three 13's is prime. [De Geest]

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