46149domain: NAppears in sequencesa(n) = (1/3)*(2 + Sum_{k=0..n} C(3k,k)).at n=7A024719Number of active (ON, black) cells at stage 2^n-1 of the two-dimensional cellular automaton defined by "Rule 525", based on the 5-celled von Neumann neighborhood.at n=7A272739