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## The answer has to be divisible by 9 (Score:1)

The sum of the digits of a number mod 9 is always the number mod 9. The sum of the digits of 2*$n and 3*$n is the same, which means that mod 9, 2*$n and 3*$n are the same, which means that $n is 0 mod 9, so $n is divisible by 9.

This should improve your speed by a factor of 3. :-)

## Re:The answer has to be divisible by 9 (Score:1)

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