67
The smallest prime number, of course, is 2. The smallest prime number whose digits add up to 2 is, of course, 2. The next-smallest is 11. It is left as an exercise for the reader to determine whether the other numbers whose digits add up to 2 (e.g. 101, 1001, 10001) are prime.
13
3 is a prime number, which means it can only be multiplied by itself or by 1. 1x3 =3, or 3x1 is 3. The number 3 adds to be 6 twice; 2 x 3 = 6.
3 is a Prime number, which means it can only be multiplied by itself or by 1. 1x3 =3, or 3x1 is 3. The number 3 adds to be 6 twice; 2 x 3 = 6.
Any number adds to 15.
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44
The smallest prime number, of course, is 2. The smallest prime number whose digits add up to 2 is, of course, 2. The next-smallest is 11. It is left as an exercise for the reader to determine whether the other numbers whose digits add up to 2 (e.g. 101, 1001, 10001) are prime.
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13
199 and 11
If the digit sum of a number adds up to 9 then it is divisible by 9.
3619
3 is a prime number, which means it can only be multiplied by itself or by 1. 1x3 =3, or 3x1 is 3. The number 3 adds to be 6 twice; 2 x 3 = 6.
3 is a Prime number, which means it can only be multiplied by itself or by 1. 1x3 =3, or 3x1 is 3. The number 3 adds to be 6 twice; 2 x 3 = 6.
Any number whose digital sum adds up to 9 is also a multiple of 9.
999