2092819domain: NAppears in sequencesNumber of (n+2)X(1+2) 0..3 arrays with every 3X3 subblock row and column sum not equal to 0 1 3 6 or 7 and every 3X3 diagonal and antidiagonal sum equal to 0 1 3 6 or 7.at n=16A252150a(n) = n! * (n+1)! * Sum_{k=0..n} (-1)^k/(k! * (k+1)!).at n=6A368853