503216domain: NAppears in sequencesNumber of 4 X n (0,1) matrices such that each row and each column is nondecreasing or nonincreasing.at n=27A086114Number 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.at n=6A356853