Entering 16 digit numbers

At work we continually copy and paste 16 digit numbers but I have not been able to figure out why excel inputs an extra 0 at the end of the 16 digit number. We have to use excel to speed up our work. Can someone help please.

You have to be careful when you work with numbers that long in Excel. Stored as a number, Excel is limited to storing 15 digits (as is any other program that uses standard double precision to store numbers). Almost always, when people are trying to use numbers that long, the numbers are invoice numbers or part numbers or the like, which don't need to be stored as numbers. You'll probably be better off getting Excel to treat those numbers as text strings rather than numbers.