Posted by **mima** on Thursday, April 12, 2012 at 12:13am.

the sum of the digits of a two digit prime number is substracted from the number. prove that the difference cannot be a prime number.

- math -
**Steve**, Thursday, April 12, 2012 at 10:42am
adding the digits produces a result that is the remainder when the number is divided by 9.

So, assuming that the prime number p = 9m+n

the sum of the digits is also n

so, p-n = 9m, not a prime

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