/\b(\d)/${1}000000000000/
/\b(\d{2})/${1}00000000000/
/\b(\d{3})/${1}0000000000/
/\b(\d{4})/${1}000000000/
/\b(\d{5})/${1}00000000/
...

##</code><code>##

/(?<=\b\d)$/000000000000/
/(?<=\b\d{2})$/00000000000/
/(?<=\b\d{3})$/0000000000/
/(?<=\b\d{4})$/000000000/
/(?<=\b\d{5})$/00000000/
/(?<=\b\d{6})$/0000000/
...