Iam a number that is greater than 600 but less than 700. the sum of my digits is 18 and i'm not divisible by 2, 5,7, or 11. what number am i?

I thought about this for a while and then recognized that this number is possibly divisible by {3, 4, 6, 8, 9, 10, 12, etc.}

So I look for possible sets of 3 numbers here that add up to 18.  The first such set I recognized was {4, 6, 8}.  These digits do add up to 18.  Unfortunately, 468 is not in the desired range (600,700).  

Thus, I could try either {6, 4, 8} or {6, 8, 4}.

There may be other combinations of 3 numbers (which must add up to 18).

Test 684.  Is 684 between 600 and 700, not including 600 or 700?  YES.

Is the sum of {6, 4, 8} equal to 18?  YES.   So, 648 is one possible answer.  Are there others?

No a triangle cannot be formed because when you add the two smallest number together (which would be 11) the have to be bigger than the number it is "against" ( which would be 12)