lol

lol.clj

(defn divides? [bottom top]
  (zero? (mod top bottom)))

(def naturals (iterate inc 1))

(defn multiples-of
  ([n]
   (map #(* n %) (rest naturals)))
  ([n max]
   (take-while #(<= % max) (multiples-of n))))

(defn combine-multiples [current-base largest composites-so-far]
  (clojure.set/union
    composites-so-far
    (set (multiples-of current-base largest))))

(defn composites [largest]
  (reduce
    (fn [composites-so-far current-base]
      (if (contains? composites-so-far current-base)
        composites-so-far
        (combine-multiples current-base largest composites-so-far)))
    #{}
    (range 2 (/ largest 2))))

(defn primes [largest]
  (clojure.set/difference (set (range 2 largest)) (composites largest)))