It was a famous problem for many years until a physics genius solved it all the way to infinity.
Featuring author Alex Bellos more links below.

Extras from this interview:    • The Four 4s (extra footage)  

More Numberphile videos with Alex: http://bit.ly/Bellos_Playlist

Alex's recent book about puzzles (including the Four 4s): http://amzn.to/2jRo0n2
More Alex books: http://bit.ly/BellosBooks

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