Metric properties in Berggren tree of primitive Pythagorean triples

Abstract

A Pythagorean triple is a triple of positive integers $(x,y,z)$ such that $x^2+y^2=z^2$. If $x,y$ are coprime and $x$ is odd, then it is called a primitive Pythagorean triple. Berggren showed that every primitive Pythagorean triple can be generated from triple $(3,4,5)$ using multiplication by uniquely number and order of three $3\times3$ matrices, which yields a ternary tree of triplets. In this paper, we present some metric properties of triples in Berggren tree. Firstly, we consider primitive Pythagorean triple as lengths of sides of right triangles and secondly, we consider them as coordinates of points in three-dimensional space.