1=1
{{subst:subst}}Exp B/running |x=1 |n={{subst:#expr:{{{n}}}+1}} |term={{subst:subst}}exponent|{{{x}}}|{{{n}}}}}/{{subst:subst}}factorial|{{{n}}}}} |sum={{{sum}}}+{{{term}}} |value={{subst:expr1}}{{{sum}}}+{{{term}}}{{subst:rightbraces1}} }}

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