(let ((string "123   456"))
  (remove nil (mapcar (lambda (item)
                        (ignore-errors (parse-integer (coerce item 'string))))
                      (nsplit-list-on-indicator (coerce string 'list)
                                                (lambda (a b) (not (equiv (digit-char-p a) (digit-char-p b))))))))
--> (123 456)