19
This number is a prime.
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19 is the smallest prime such that there exists a multiple having the same sum of
digits as its digital root, e.g., 75 = 19 x 3; 7 + 5 = 12, 1 + 2 = 3, and 3 = 3. [Kholdi]
Submitted: 2010-07-23 19:12:29; Last Modified: 2020-05-26 22:17:35.
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