22.[Stan2012a]*Ch. 3 Exer. 185(j)
Let SnW be the set of permutations of n ordered by the
weak Bruhat order. Characterize the intervals of SnW
that are distributive lattices and compute their total number.
The values for 1≤n≤8 are
1, 2, 16, 124, 1262, 15898, 238572, 4152172.