Welcome to CL! One of the first and hardest things to get used to is that CL does not operate like Python or other typical languages like that. It does not operate sequentially (except within a when … otherwise statement), it does not do native calculation operations (you need to define functions or use numeric value), and so on. So some things will be more complex than it feels like it needs to be - and some other things will be much simpler.
There is list support within CL, including list comprehensions, which will make things significantly easier. Here is a cleaned up example of what you have above - once you get the hang of it, the copy/paste part for the 20 cells is not that big a deal.
Here is a link in the Resources category that explains everything about how to use lists.
Feel free to ask for help on specific things that you are trying to make work.