Triangular array T read by rows: T(r,c) is the number of double permutations of the integers from 1 to r which have exactly c different values visible when viewed from the left, in the sense that a higher number hides a lower one.

A309053

Triangular array T read by rows: T(r,c) is the number of double permutations of the integers from 1 to r which have exactly c different values visible when viewed from the left, in the sense that a higher number hides a lower one.