Parity reversing involutions on plane trees and 2-Motzkin paths
European Journal of Combinatorics
Analytic Combinatorics
Note: Wiener index versus Szeged index in networks
Discrete Applied Mathematics
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It is a known fact that the Wiener index (i.e. the sum of all distances between pairs of vertices in a graph) of a tree with an odd number of vertices is always even. In this paper, we consider the distribution of the Wiener index and the related tree parameter ''internal path length'' modulo 2 by means of a generating functions approach as well as by constructing bijections for plane trees.