57127667585domain: NAppears in sequencesNumber of (2+2) X (n+2) 0..3 arrays with every 3 X 3 subblock row and diagonal sum equal to 1, 2, 4, 6 or 7 and every 3 X 3 column and antidiagonal sum not equal to 1, 2, 4, 6 or 7.at n=21A252560