(defn rot90
  "Rotate rows 90 degrees clockwise."
  [rows]
  (mapv reverse (apply map list rows)))
 
(defn add-row
  "Adds new row, values starting at bottom left value + 1."
  [rows]
  (let [n (-> rows last first dec)
        width (-> rows first count)
        row (take width (iterate dec n))]
    (conj rows row)))
 
(defn solve
  [n]
  (let [seed [[(* n n)]]
        idx (* 2 (dec n))
        step (comp add-row rot90)]
    (-> (iterate step seed) (nth idx) rot90 rot90)))
 
(println (solve 5))

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