crontab -e command and append a line to the schedule
First that comes to mind is this:
00 14 * * 1,3,5 /fun/fun.sh
Suppose you have asked for as this form of schedule will run on Mon/Wed/Fri and then skip two days.
A more proper form will be this one:
00 14 1,3,5,7,9,...,31 * * /fun/fun.sh