21335779
This number is a prime.
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Write all the single-digit primes (2 3 5 7). Then write the only digits a prime can end with (1 3 7 9). Put the second set of digits between the first set (2 (1) 3 (3) 5 (7) 7 (9)) to get 21335779. [Earls]
Submitted: 2006-12-17 11:44:32; Last Modified: 2008-01-30 17:28:00.
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