Euler problem 10 in Clojure

euler-p10.clj

(defn sieve-of-era
  "Generate the primes upto N based on sieve of erastothenes"
  ([num] (sieve-of-era [] num (range 2 num)))
  ([primes num sieve]
  (let [x (first sieve)]
    (def divisible? (fn [divisor num] (zero? (rem num divisor))))
    (def remaining (fn [coll x] (remove (partial divisible? x) coll)))
    ;optimisation - enough to remove until current prime ^ 2 < limit
    (if (>= (* x x) num) (concat primes sieve)
      (recur (conj primes x) num (remaining (rest sieve) x))))))

(defn euler-10 [num]
  (reduce + (sieve-of-era num)))

(time (println (euler-10 2000000)))