Gessel, Ira M., and Yan Zhuang. “Counting Permutations by Alternating Descents”. The Electronic Journal of Combinatorics 21, no. 4 (October 30, 2014): P4.23. Accessed March 15, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v21i4p23.