Abstract. For non-negative integers r and s with r + s = n − 1, let [b r a s ] denote the number of permutations π ∈ Sn which have the property that π(i) > i if, and only if, i ∈ [r] = {1, . . . , r}. Answering a question of Clark and Ehrenborg (2010), we determine asymptotics on [b r a s ] when r = (n − 1)/2 :We also determine asymptotics on [b r a s ] for a suitably related r = Θ(s) → ∞. Our proof depends on multivariate asymptotic methods of R. Pemantle and M. C. Wilson.We also consider two applications of our main result. One, we determine asymptotics on the number of permutations π ∈ Sn which simultaneously avoid the vincular patterns 21-34 and 34-21, i.e., for which π is order-isomorphic to neither (2,1,3,4) nor (3, 4, 2, 1) on any coordinates 1 ≤ i < i+1 < j < j +1 ≤ n. We also determine asymptotics on the number of n-cycles π ∈ Cn which avoid stretching pairs, i.e., those for which 1 ≤ π(i) < i < j < π(j) ≤ n.

Agradeço ao meu orientador, Professor Toscano, ao Daniel V. Tausk eà Mariana por toda a ajuda, paciência e disposição para ouvir e discutir. Sou muito grato tambémà Da. Johanna W. Smit, cujo apoio me foi indispensável durante os meus anos de graduação e mestrado.