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Solution to Puzzle 39.  PRIME NUMBERS

Prime numbers are numbers whose only divisors are one and itself.  For example, 31 is a prime number because its only divisors are 1 and 31.  However, 12 is not a prime number because it can be divided by 1, 2, 3, 4, 6, or 12. 

There are NO PRIME NUMBERS among those 9-digit numbers that can be formed by rearranging the digits in the number: 

1  2  3  4  5  6  7  8  9

Any number whose digits sum up to a number divisible by 3 is divisible by 3.  The above number has this property, and therefore any number formed by rearranging the digits of this number is divisible by 3 and therefore not a prime number.

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Aha! Gotcha : Paradoxes to Puzzle and Delight

Author:  Martin Gardner

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