Major Index on Catalan Combinatorics

We study the two statistics, the inversion number and the major index, on Catalan combinatorial objects such as $r$-Dyck paths, $r$-Stirling permutations, non-crossing partitions, Dyck tilings, and symmetric Dyck paths. We show that they are equidistributed with the inversion number or the major index on Dyck paths.