happy-number-seq

;; BY CLAUDE:

(defun happy-step (n)
  (reduce #'+ (mapcar (lambda (d) (* d d)) (digits n))))

(defun 

 (n &optional acc)
  "Sequenz bis Fixpunkt 1 oder bis Zyklus erkannt."
  (let ((acc (or acc (list n))))
    (let ((next (happy-step n)))
      (if (member next acc)
          (append acc (list next))   ; Zyklus: letztes Element zeigt wohin
          (happy-seq next (append acc (list next)))))))


(happy-seq (rnd-pick (happy-numbers 100)))

(list-plot (loop repeat 10
                   collect (flatten (happy-seq  (rnd-pick (happy-numbers 300)))))
           :join-points t)