237109domain: NAppears in sequencesNumber of active (ON, black) cells at stage 2^n-1 of the two-dimensional cellular automaton defined by "Rule 813", based on the 5-celled von Neumann neighborhood.at n=8A273639G.f. A(x) satisfies A(x) = 1 / ((1 + x) * (1 - x * (1 + x + x^2) * A(x^3))).at n=21A367717