I really enjoyed the puzzles! It is certainly cool to have to input the numbers yourself, but I feel like there needs to be a verification step that at some point in the program the stack matches the level's requirement. Right now it's too easy to cheat the system (I did them all legit, I swear!). And yeah I only needed the ram for the last level because it was the only one where I wanted to meet the "stack must match level input at some point" and needed to just keep the ones digit away from the others while I did calculations.
The other thing I found myself wishing for was more visuals like highlighting what column was being evaluated and maybe skipping of empty columns faster.
In other words, the game design is a solid foundation and I just would love more strictness and more levels! More ram levels :D