https://www.codeeval.com/open_challenges/4/

CE4.clj

(ns sumofprimes)

(def primes "Infinite, lazy sequence of prime numbers."
  ((fn step [m n]
     (or
       (some-> (get m n) (-> (->> (reduce #(update %1 (+ %2 n) conj %2) (dissoc m n))) (step (inc n))))
       (-> (assoc m (* n n) (list n)) (step (inc n)) (->> (cons n) (lazy-seq)))
       )) {} 2))

; without threading
(def optimus "Infinite, lazy sequence of prime numbers."
  ((fn step [m n]
       (if-let [factors (get m n)]
         (recur (reduce #(update %1 (+ %2 n) conj %2) (dissoc m n) factors) (inc n))
         (lazy-seq (cons n (step (assoc m (* n n) (list n)) (inc n))))
       )) {} 2))
     
(println (reduce + (take 1000 primes)))