(defun increment-number-at-point (&optional arg)
  "Increment a number at point."
  (interactive "*P")
  (let* ((bounds (bounds-of-thing-at-point 'word))
         (beg (car bounds))
         (end (cdr bounds))
         (num (string-to-number (buffer-substring beg end)))
         (incr (cond ((null arg) 1)
                     ((listp arg) -1)
                     (t arg)))
         (value (+ num incr)))
    (delete-region beg end)
    (insert (format "%d" value))))
(global-set-key "\C-zi" 'increment-number-at-point)