Golden number, is an irrational number represented by the Greek letter φ (phi). We all know the drawing that Leonardo da Vinci made to illustrate the book 'The Divine Proportion' by the mathematician Luca Pacioli, which proposes a perfect man (homo quadratus) in which the relationships between the different parts of the body are based on the number of gold, as shown in the famous drawing.

In the human body. It turns out that the ratio of the man's height to the distance from the navel to the tip of the hand is the golden number. Perhaps the most striking is the one related to the navel: if the total height of a man is divided by the distance from the navel to the feet, we obtain the golden number.

The plastic arts. Appears in the 5th century BC in Athens, the Greeks knew it and used it in architectural and sculptural designs.
In the music. In various Mozart piano sonatas, the ratio between the development of the theme and its introduction is as close as possible to the ratio of the golden number.
In mathematics. Gold numbers are present in all regular or semi-regular geometric objects in which there is pentagonal symmetry.
In nature. There are many elements related to the golden section or the Fibonacci sequence that have a great similarity