qwtel

// emits a value after `init` ms, then after `init * exp` ms, then `init * exp * exp` ms, etc.
function expInterval(init, exp) {
  return Observable.create((observer) => {
    let n = init;
    let id;

    function next() {
      observer.next(n);
      n *= exp;
      id = setTimeout(next, n);