425600domain: NAppears in sequencesa(n) = n!! mod n!!!at n=20A217649Number of (3+2) X (n+2) 0..3 arrays with every 3 X 3 subblock row and diagonal sum equal to 0 2 3 6 or 7 and every 3 X 3 column and antidiagonal sum not equal to 0 2 3 6 or 7.at n=17A252535