Statistics on monotonically ordered non-crossing partitions

Abstract: We study some combinatorial statistics defined on the set NC^{mton}(n) of monotonically ordered non-crossing partitions of {1,...,n}, and on the set NC_2^{mton}(2n)$ of monotonically ordered non-crossing pair-partitions of {1,...,2n}. An important fact used in the calculations is that one has a natural and very convenient structure of rooted tree on the union of the NC^{mton}(n)'s, and likewise for the union of the NC_2^{mton}(2n)'s. Unlike in the analogous results known for unordered non-crossing partitions, the computations of expectations and variances for natural block-counting statistics on NC^{mton}(n) and for the expectation of the area statistic on NC_2^{mton}(2n) turn out to yield a logarithmic regime.