We study the descent distribution over the set of centrosymmetric
permutations that avoid the pattern of length 3. Our main tool in the most
puzzling case, namely, Ï„=123 and n even, is a bijection that associates
a Dyck prefix of length 2n to every centrosymmetric permutation in S2n​
that avoids 123.Comment: 17 pages, 6 figure