As I was going to St. Ives, I met a man with seven wives. Each wife had seven sacks. Each sack has seven cats. Each cat had seven kits. Kits, cats, sacks, and wives, How many were going to St. Ives?
Literally, only "I" was going to St. Ives. But suppose they were going in the same direction? You could easily figure how many people, sacks, and critters I met: 1 +7 +7^2 + 7^3 + 7^4 = (7^5 - 1)/(7 - 1) = 2801. Add "me" and you get 2802.