256796921471domain: NAppears in sequencesNumber of (3+1)X(n+1) 0..1 arrays x(i,j) with row sums sum{x(i,j), j=1..n+1} nondecreasing, and column sums sum{i*x(i,j), i=1..3+1} nondecreasing.at n=21A233064