31000...00001 (53-digits)

This number is a prime.

                  310 0000000000 0000000000 0000000000 0000000000 0000000001

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If we concatenate the day and month of the 31 January, we get 3101 (a composite number). If zeros are inserted between the day and the year, 49 are required before a prime number is reached. This is more than for any other day of the year, with the possible exception of 10 January. [Hartley]