problem_3.clj

(defn primes
  [n]
  (letfn [(multiple-of?
           [p]
           (= 0
              (mod n p)))
          (sieve
           [ps]
           (let [p (first (rest ps))]
             (if (> (* p p)
                    n)
               ps
               (recur (remove #(multiple-of? %)
                              ps)))))]
    (sieve (range 2 (+ n 1)))))

(primes 30)