Phi

Phi () is defined as the limit of the ratio of successive terms of the Fibonacci sequence. It can be shown that this limit is a solution to the quadratic equation . Since the terms of the fibonacci is positive, we take the positive solution of the quadratic and define .

Phi is also known as the Golden Ratio. It was commonly believed by the Greeks to be the most aesthetically pleasing ratio between side lengths in a rectangle.

The first few digits of Phi in decimal representation are: 1.61803398874989...