Number of permutations p of [2n+1] such that at most one element of {p(1),...,p(i-1)} is between p(i) and p(i+1) for all i <= 2n and p(2n+1) = n+1.

A356853

Number of permutations p of [2n+1] such that at most one element of {p(1),...,p(i-1)} is between p(i) and p(i+1) for all i <= 2n and p(2n+1) = n+1.