Ayache, Ahmed; Sharif, Walied H.; Vu Dinh Hoa A formula about tree. (English) Zbl 1116.05018 Vietnam J. Math. 33, No. 3, 343-348 (2005). Summary: Let \(G\) be a tree. We prove that for any vertex \(v\) of \(G\) \[ |V|+ \sum_{q\in V}[d(q)-2]l(v,q)=1 \] where \(d(q)\) is the degree of the vertex \(q\), and \(l(v,q)\) is the distance between \(v\) and \(q\) in \(G\). This result enables us to derive a formula concering the average distance for some particular trees. MSC: 05C05 Trees PDFBibTeX XMLCite \textit{A. Ayache} et al., Vietnam J. Math. 33, No. 3, 343--348 (2005; Zbl 1116.05018)