A Combinatorial Interpretation for a Super-Catalan Recurrence
نویسندگان
چکیده
Nicholas Pippenger and Kristin Schleich have recently given a combinatorial interpretation for the second-order super-Catalan numbers (un)n 0 = (3; 2; 3; 6; 14; 36; :::): they count \aligned cubic trees" on n internal vertices. Here we give a combinatorial interpretation of the recurrence un = Pn=2 1 k=0 n 2 2k 2 2 uk : it counts these trees by number of deep interior vertices where deep interior means \neither a leaf nor adjacent to a leaf".
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