  The total activity of the single-seeded cellular rule 150 automaton does not
follow a one-step iteration like other elementary cellular automata, but can be
solved as a two-step vectorial, or string, iteration, which can be viewed as a
generalization of Fibonacci iteration generating the time series from a
sequence of vectors of increasing length. This allows to compute the total
activity time series more efficiently than by simulating the whole
spatio-temporal process, or even by using the closed expression.
