It will need to be just a little more complex than a single 555. For the first pulse, when the timer times out after "n", it will trigger again, as tehpulse is still active. You may be able to use a capacitor on the trigger pin so that the timer only fires when the input makes a high to low transition. In that case, a 555 configured as a one-shot with a period of "n" would be appropriate.
You'll also need to invert your input signal, as the 555 fires in a low pulse.