When the number of teeth is not a whole multiple of the number of arms, you can rotate the rings to get a good match for the climbing of a chain. I cannot remember a case where I would not make a ring and derailleur combination work. On my Brompton I currently have 50-34-20. Before I had 50-32-20 and earlier 50-34-24. On the full-size bike I have 4 chainrings and again I experimented with a multitude of combinations. You could make all of them work.