calculate prime numbers and prime factors with clojure

primes.clj

(ns primes.core)

(defn- primes
  "returns a lazy list of prime numbers via the sieve of eratosthenes"
  ([]
   (primes (iterate inc 2)))
  ([[head & tail]]
   (cons head
         (lazy-seq (primes (remove #(and (not= % head)
                                         (zero? (mod % head))) tail))))))

(defn factors
  "return all prime-factors of a number"
  ([n]
    (factors n [] (primes)))
  ([n acc prim]
   (let [p (first prim)]
     (cond
       (= n p)           (conj acc p)
       (zero? (mod n p)) (factors (quot n p) (conj acc p) prim)
       :else             (factors n acc (rest prim))))))