It becomes obvious when you know closed form expression for Fibonacci numbers as a sum of powers of phi (which I'm sure Tao is aware of). I was taught that in h

It becomes obvious when you know closed form expression for Fibonacci numbers as a sum of powers of phi (which I'm sure Tao is aware of). I was taught that in high school. The only reason this wouldn't be obvious to Tao is if he was working on much harder problems for so long that he forgot the basic stuff.