Was anyone else struck by the notion of remembering 20 items that were brainstormed while bike riding? I could probably remember a dozen items to get at the grocery store, but I don't know that I could simultaneously generate creative ideas and remember a list of unrelated ideas (unlike groceries, which can be grouped by category).
Perhaps he just brainstormed a few dozen ideas, and these were the 20 that he remembered most easily when he got home. But given what we know of Don Knuth, it wouldn't be surprising if he were easily able to generate and remember longer lists of things than most people!