Retry Celery tasks with exponential back off

For a task like this:

from celery.decorators import task

@task()
def add(x, y):
    if not x or not y:
        raise Exception("test error")
    return self.wait_until_server_responds(

if it throws an exception and I want to retry it from the daemon side, how can apply an exponential back off algorithm, i.e. after 2^2, 2^3,2^4 etc seconds?

Also is the retry maintained from the server side, such that if the worker happens to get killed then next worker that spawns will take the retry task?