Numberphile Explains the Unsolvable Graceful Tree Problem

Watch the math expert try and fail to solve the conundrum that has been around since 1967.
Loukia Papadopoulos

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.