  Le n be any positive integer. A hyperbinary expansion of n is are
presentation of n as sum of powers of 2, each power being used at most twice.
In this paper we study some properties of a suitable edge-coloured and
vertex-weighted oriented graph A(n) whose nodes are precisely the several
hyperbinary representations of n. In particular, we identify those integers m
in N such that the fundamental group of A(m) is abelian.
