Huh, JiSun, and SeungKyung Park. “Generalized Small Schröder Numbers”. The Electronic Journal of Combinatorics 22, no. 3 (July 31, 2015): P3.14. Accessed March 27, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v22i3p14.