Sophie Germain primes

germain.clj

(require '[clojure.math.numeric-tower :refer [sqrt]])

(defn smallest-divisor [n]
  (find-divisor n 2))

(defn divides? [a b]
  (= (mod b a) 0))

(defn find-divisor [n test-divisor]
  (cond (> (sqrt test-divisor) n) n
        (divides? test-divisor n) test-divisor
        :else (find-divisor n (+ test-divisor 1))))

(defn prime? [n]
  (= n (smallest-divisor n)))

(defn germain? [n]
  (prime? (inc (* 2 n))))

 (filter (every-pred germain? prime?) (range 2 100))

=> (2 3 5 11 23 29 41 53 83 89)