Question 827120
<pre>
If all four non-primes can be the same number, 
then the answer is:

The four non-prime integers are all 1's.

The greatest common factor of 1 and 1 is 1, and the
sum of the four 1's is 4, which is as low as possible.
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If you mean that they all must be different, then,

1,4,9,25

Their sum is 39, which is as low as possible.

Edwin</pre>