135793domain: NAppears in sequencesa(0) = 1, a(1) = 3; for n>1, a(n) = n*a(n-1) + (-1)^n.at n=8A110149Number of strings of n numbers x(i) in -8..8 with sums of x(i) and of x(i)*x(i+1) both zero.at n=6A183943