function identity(x) { return x; }
Rx.Observable.create(o => {
      console.log('subscribing');
      o.onError(new Error('always fails'));
  }).retryWhen(function (attempts) {
      return Rx.Observable.range(1, 3)
        .zip(attempts, identity)
        .flatMap(function (i) {
          console.log('delay retry by ' + i + ' second(s)');
          return Rx.Observable.timer(i * 1000);
      });
  }).subscribe();
  
/*
subscribing
delay retry by 1 second(s)
subscribing
delay retry by 2 second(s)
subscribing
delay retry by 3 second(s)
subscribing
*/