let a, b and c be 3 numbers whose Greatest Common Factor is 13.
This means that all a, b, and c are multiples of 13, and the three of them have no other common factor (except1)
So we can construct a, b and c as follows:
a=13*2*3, b=13*2*5, c = 13*7
a=78, b=130, c=91
Answer: {78, 130, 91}