Ring of Primes http://coj.uci.cu/24h/problem.xhtml?abb=1196

ring_of_primes.clj

(ns ring-of-primes
  (:gen-class))

(defn prime?
  [n]
  (and (> n 1)
       (not-any? #(zero? (mod n %)) (range 2 (inc (int (Math/sqrt n)))))))

(defn neighbours
  [xs ring]
  (for [x xs :when (prime? (+ x (last ring)))]
    [(disj xs x) (conj ring x)]))

(defn lazy-ring-of-primes
  [stack]
  (when-let [[xs ring] (peek stack)]
    (if (empty? xs)
      (if (prime? (+ (first ring) (last ring)))
        (cons  ring (lazy-seq (lazy-ring-of-primes (pop stack))))
        (recur (pop stack)))
      (recur (reduce conj (pop stack) (neighbours xs ring))))))

(defn ring-of-primes
  [n]
  (lazy-seq (lazy-ring-of-primes [[(into #{} (range 2 (inc n))) [1]]])))

(defn -main [& args]
  (let [[n m] (map #(Integer/parseInt %)  args)]
    (when-not n (throw (Exception. "Size of ring not specified")))
    (doseq [ring (if m (take m (ring-of-primes n)) (ring-of-primes n))]
      (println ring))))