On a Graph Connecting Hyperbinary Expansions
  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. 
M. Brunetti and A. D'Aniello
math.CO