Rule: a dead cell turns ON if exactly 1 of its 4 orthogonal neighbors is ON.
Starting from a single cell, the pattern grows fractally — population a(n) = (4/3)(2^n - (-1)^n/2^n... ) actually follows a quasi-power law related to 2^n.
Total cells ON at generation n follows A(n) ~ C·2^n with fractal corrections.