1, 11, 21, 1211, 111221, 312211, 13112221, …
This sequence was the favorite pattern of my former department chair, Nelson Rich. I thought he invented it, but a quick search on the internet reveals that it’s pretty easy to find if you search for the first few terms.
But don’t do that! It’s a sneaky one, but fun to try and figure out.
Try saying the digits out loud. This is an aural/visual sequence rather than a numeric one.
And yes, I did have to look up aural to make sure I was using it correctly.