Explanation:
First, find the vertex. The x coordinate is -b/2a, or 12/-4=-3. Plug this back in to get -18+36-21 or -3, so the vertex is (-3, -3). Now, slowly make the x -2, -1, 0, 1, on and on. Because parabolas are symmetric along the vertex, they will have the same values as -4, -5, -6, on and on.