Clearly, all integer values of r satisfy the polinom being integer.

If we are lookin for fraction , it nust be n/3, n being an integer.

Then the polynom becomes ** 1/9 *n*(n^2+10*n-27).**

n^2+10*n =n*(n+10), divisible by 9** iff n=0 mod 9 or 8 mod 9.**

Therefore ** r= any integer**

or r= ** 8/3,17/3.26/3 ..**.

and** -1/3, -10/3, -19/3... etc.**

*Edited on ***March 17, 2013, 6:24 am**