Project Euler Problem 10 は Clojure でやっても 100ms 未満で計算できるはず。

pe10.clj

(ns tnoda.pe10)

(defn- sieve
  "Returns an array of primes below len. Retrieved from
https://github.com/tnoda/tnoda.math.prime."
  [^long len]
  (let [n len
        not-prime (doto (boolean-array n)
                    (aset 0 true)
                    (aset 1 true))
        primes (long-array n)]
    (loop [p 0, i 2]
      (if (< i n)
        (if (aget not-prime i)
          (recur p (inc i))
          (do
            (aset primes p i)
            (loop [j (* i i)]
              (when (< j n)
                (aset not-prime j true)
                (recur (+ j i))))
            (recur (inc p) (inc i))))
        (let [ps (long-array p)]
          (System/arraycopy primes 0 ps 0 p)
          ps)))))

(defn solve
  []
  (let [ps (longs (sieve 2000000))]
    (areduce ps i ret 0 (+ ret (aget ps i)))))

;; tnoda.pe10> (time (do (solve) nil))
;; "Elapsed time: 41.039 msecs"
;; nil