226200domain: NAppears in sequencesNumber of active (ON, black) cells at stage 2^n-1 of the two-dimensional cellular automaton defined by "Rule 401", based on the 5-celled von Neumann neighborhood.at n=8A271804a(n) = phi(12^n-1), where phi is Euler's totient function (A000010).at n=4A366711