31000...00001 (53-digits)

This number is a prime.

                  310 0000000000 0000000000 0000000000 0000000000 0000000001

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]