condotti's solution to https://4clojure.com/problem/138

gistfile1.clj

(fn [l u]
  (let [s (apply str (take-while #(<= % u) (iterate #(* % %) l)))
        d (int (Math/ceil (Math/sqrt (count s))))
        n (concat (seq s) (repeat (- (* d d) (count s)) \*))
        m (loop [m {} sx n
                 r (if (even? d) (- d 2) (dec d)) c (- d 1)
                 dr (mapcat #(repeat (* % 2) (if (even? %) -1 1)) (range))
                 dc (mapcat #(repeat (inc (* % 2)) (if (even? %) 1 -1)) (range))]
            (if (empty? sx) m
                (recur (assoc m [r c] (first sx)) (rest sx)
                       (+ r (first dr)) (+ c (first dc))
                       (rest dr) (rest dc))))]
    (for [r (range (dec (* d 2)))] (apply str (for [c (range (dec (* d 2)))] (m [r c] \space))))))