How to schedule todo in org for every even day, and similar for every odd day?

Question

I would like to schedule a todo item every Monday, Wednesday, Friday.

I followed this one: Org-mode schedule 1 event for multiple days?

and get something like this:

* stuff to do
SCHEDULED: <Monday 4/5/2020 +1w><Wed 6/5/2020 +1w><Fri 8/5/2020 +1w>

This doesnt show up on my agenda. So I think the way I write it down is wrong. Could anyone give some pointers?

Answer 1

One idea would be to create a custom function that tests for specified days of the week. The following example is hard-coded to return t for Monday (i.e., 1), Wednesday (i.e., 3) and Friday (i.e., 5).

This can be used in an org-mode file such as:

* My Task
  SCHEDULED: <%%(diary-monday-wednesday-friday date)>

Or, it can be used in a diary file and seen in the agenda view with (setq org-agenda-include-diary t) using a diary entry such as:

%%(diary-monday-wednesday-friday date) Monday or Wednesday or Friday

CODE:

(require 'calendar)

;;; ORG-MODE:  * My Task
;;;              SCHEDULED: <%%(diary-monday-wednesday-friday date)>
;;;
;;; DIARY:  %%(diary-monday-wednesday-friday date) Monday or Wednesday or Friday
;;;
;;; See also:  (setq org-agenda-include-diary t)
;;;
;;; (diary-monday-wednesday-friday '(5 7 2020)) => nil
;;;
;;; (diary-monday-wednesday-friday '(5 8 2020)) => t
;;;
;;; 0 => Sunday
;;; 1 => Monday
;;; 2 => Tuesday
;;; 3 => Wednesday
;;; 4 => Thursday
;;; 5 => Friday
;;; 6 => Saturday
;;;
(defun diary-monday-wednesday-friday (date)
"Return `t` if DATE is a Monday, Wednesday or Friday."
  (let ((day-of-week (calendar-day-of-week date)))
    (member day-of-week '(1 3 5))))

Answer 2

If this is really an appointment reminder, rather than a scheduled task, then the easiest thing to do is to forego the SCHEDULED: marker and just have the three timestamps listed (I like putting the timestamps on different lines, but you can put them on a single line if you want):

* stuff to do
  <Monday 4/5/2020 +1w>
  <Wed 6/5/2020 +1w>
  <Fri 8/5/2020 +1w>

Assuming that the file is indeed an agenda file, stuff to do will appear in the agenda every Monday, Wednesday and Friday.