    public static void main(String[] args) {

        Flowable<Long> flowable = Flowable.range(1, 5)
                .filter(i -> i % 2 == 0)
                .flatMap(i -> interval(i, TimeUnit.SECONDS));

        flowable.subscribe(
                l -> log.info("Even time intervals {}", l),
                ex -> log.error("Error {}", ex.getMessage())
        );

        hold(30000);