76155945522domain: NAppears in sequencesNumber of (n+2) X (3+2) 0..3 arrays with every 3 X 3 subblock row and column sum not equal to 0 2 5 6 or 7 and every 3 X 3 diagonal and antidiagonal sum equal to 0 2 5 6 or 7.at n=21A252418