You can use translate for this. I'm attaching an IP 2003 template where the default value of the first field on the form is set to display yyyymmddhhmmss:
translate(translate(translate(now(), "T", ""), ":", ""), "-", "")
is the formula. If you want only digits for year, you can use substring to remove the first two (see the second field on the form):
substring(translate(translate(translate(now(), "T", ""), ":", ""), "-", ""), 3)