prime-table.clj

;
; Generate a table of the products of prime numbers
;

(defn √ [x] 
  "Integer square root of x"
  (int (Math/sqrt x)))
  
(defn prime? [x]
  "Return true if x is a prime number, using naïve trial division algorithm."
  (->>
   (range 2 (inc (√ x)))
   (map (fn [d] (/ x d)))
   (not-any? integer?)))
  
(defn prime-numbers []
  "A lazy seq of prime numbers"
  (lazy-seq
   (->>
    (range)
    (drop 2)
    (filter prime?))))
    
(defn products [xs]
  "Return a table of xs by xs and their products."
   (for [y xs]
    (for [x xs]
      (* x y))))
  
(defn format-row [row]
  (apply str 
  (map (clojure.core/format "%8d" %) row)))

(defn format-tbl [tbl]
  "Format a list of numbers and seq of seqs into a table"
   (clojure.string/join "\n" 
                        (map format-row tbl)))
   
(->>
 (prime-numbers)
 (take 6)
 (products)
 (format-tbl)
 (println))