19680277domain: NAppears in sequencesWedderburn-Etherington numbers: unlabeled binary rooted trees (every node has outdegree 0 or 2) with n endpoints (and 2n-1 nodes in all).at n=25A001190Number of n-node rooted unlabeled trees with outdegree <= 2 and exactly 1 edge at the root.at n=25A036656