-4 plus/minus square root of 15.
There are many possible answers. One such of the following: {3, 20, and 34 lots of -1}. Another is {-15, 4}
They are elements of the infinite set of numbers of the form 15*k where k is an integer.
What about it? Factorise it?
15
-231
-4 plus/minus square root of 15.
-4 plus/minus square root of 15.
-11
141
4 and 11.
-5 and -10
13
63
-273
60 AND 15
399