13075456domain: NAppears in sequencesNumber of nX6 arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, with every occupancy equal to zero or two.at n=7A221380Base-15 representation of a(n) is the concatenation of the base-15 representations of 1, 2, ..., n, n-1, ..., 1.at n=4A260865