2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/72523In this paper, we give a simple combinatorial explanation of a formula of A. Postnikov relating bicolored rooted trees to bicolored binary trees. We also present generalized formulas for the number of labeled k-ary trees, rooted labeled trees, and labeled plane trees.9 pages, 3 figures (use PSTricks)Combinatorics05A15 (Primary); 05C05, 05C30 (Secondary)text