50648domain: NAppears in sequencesa(n) = Sum_{r=0..n-1} Sum_{s=r+1..n} s! * r^(n-s).at n=7A190194Number of regions into which a figure made up of a row of n adjacent congruent rectangles is divided upon drawing diagonals of all possible rectangles (a(0)=0 by convention).at n=23A306302