In Excel, you cannot make a true number that precise. It gives 15 digits of
precision for a number. However, you can format cells as text (or precede an
entry with an apostrophe, which means the entry will be treated as text) and
enter many more than 15 numeric characters as a text string.
Either format your cell as text prior to entry or precede your number with
an apostrophe. You can not use any other number format without truncating
your data because excel has precision limit of up to 15 digits only. You
can find this other limitation in your help file by searching for the word
"Limit".