Template:Factorial!

{{subst:subst}}#ifexpr:{{{1}}}=0|{{{2}}}|{{subst:subst}}factorial!{{subst:pipe}}{{subst:subst}}#expr:{{{1}}}-1{{subst:rightbraces}}{{subst:pipe}}{{subst:subst}}#expr:{{{2}}}*{{{1}}}{{subst:rightbraces}}{{subst:rightbraces}}{{subst:rightbraces}}

Substituting this template produces one or more new substitution template calls, allowing recursive change of a page, see m:Help:Recursive conversion of wikitext.