Electrum generates the 21st address once you use the first address, the 22nd address, once you use the second address and so on.
Yes, you are correct. My bad, I didn't actually count them. I just went with what I remembered, and I was pretty sure that electrum shows (generates) addresses in batches of 20. Well, either I stumbled upon an ancient version of Electrum, or I just had a classic case of "memory corrupt" here.