Numberphile Explains the Unsolvable Graceful Tree Problem
Numberphile is back and this time he has a problem that can pretty much never be solved. It turns out that if you put odd consecutive integers starting with 1 in a designed tree that has five or more spots, you can never subtract them according to their positions without getting a repeat number.
The beauty of this trick is that it works regardless of the design of the tree. Numberphile gets creative drawing everything from serpents to ants.
The problem is actually an unsolved problem from 1967 called the graceful tree conjecture. And it works with any number of connected circles.
However, there is one caveat. There can be no loops. The video is entertaining and fun to watch although you could try this trick yourself.