I'm trying to find the generating function for this sequence:
What I know so far:
$$0\cdot x^0 + 0\cdot x^1 + 3\cdot x^2 + 0 \cdot x^3$$
So what I have to do now Is just add the two, but I'm not 100% sure how to give a closed form answer for the second sequence. From what I can see it has an arithmetic progression of $8\cdot n$, so I've gotten this:
What else do I need to do ? have I found the generating function?