rxjava 2 flapMap example in Android

Each successive flapMap takes the result from the previous one as the input, multiply it by an integer and passes it as a new input to the next flapMap. For example:
input: 2
1st flapMap: 2 * 2
2nd flapMap: 4 * 3
3rd flapMap: 12 * 4
Final result: 48

private void flapMapEx() {
    Observable.just(2)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .flatMap(new Function>() {
                @Override
                public Observable apply(Integer integer) {
                    Log.d("flatMap", integer + " * 2");
                    return multiplyInt(integer, 2);
                }
            })
            .flatMap(new Function>() {
                @Override
                public Observable apply(Integer integer) {
                    Log.d("flatMap", integer + " * 3");
                    return multiplyInt(integer, 3);
                }
            })
            .flatMap(new Function>() {
                @Override
                public Observable apply(Integer integer) {
                    Log.d("flatMap", integer + " * 4");
                    return multiplyInt(integer, 4);
                }
            })
            .subscribe(new Observer() {
                @Override
                public void onSubscribe(Disposable d) {

                }

                @Override
                public void onComplete() {
                    Log.d("flatMap", "onComplete");
                }

                @Override
                public void onError(Throwable e) {
                    e.printStackTrace();
                    Log.d("flatMap", "onError");
                }

                @Override
                public void onNext(Integer integer) {
                    Log.d("flatMap", "Final result: " + integer.toString());
                }
            });

}

private Observable multiplyInt(final Integer integer, final int mulplier) {
    //simulating a heavy duty computational expensive operation
    for (int i=0; i<1000000000; i++) {}
    return Observable.just(new Integer(integer * mulplier));
}