RxJava Fibonacci Sequence

Utils.java

public class Utils {

    public static Observable<Integer> fibonacci(int f1, int f2) {
        return Observable.range(1, 1).
                repeat().
                scan(new ArrayList<>(Arrays.asList(f1, f2)),
                        (list, tick) -> {
                            list.add(list.get(list.size() - 2) + list.get(list.size() - 1));
                            list.remove(0); //or else this becomes pretty memory inefficient eventually, right?
                            return list;
                        }
                ).map(list -> list.get(list.size() - 1));
    }
}

maybe instead of using ArrayList, Tuple will be more readable?

private static Observable<Integer> fibsStartFrom(int f1, int f2) {
        return Observable.just(true)
                .repeat()
                .scan(Tuple.create(f1, f2), (tuple, dummyTrue) -> Tuple.create(tuple.value2(), tuple.value1() + tuple.value2()))
                .map(Tuple2::value2);