This riddle starts off with a rollicking story of monsters and magic, and then gets into math. There's some logic, too, but it's really about math. While the answer is pretty darn cool, it wouldn't work if the numbers were the least bit different. Sure, sea monsters and floating cities are fantastical, but what really defies logic in this story is that they could keep chests full of pearls around for a thousand years without someone stealing any. That part is truly preposterous.