Pleeeese help.

I have a spreadsheet which I am using to store serial numbers along with
other mathematical information. The problem I am having is when I enter a
serial number with sixteen digits it changes the last digit to a 0.
seventeen digits changes the last two digits to 0s and so on. Is these
anyway to stop this happening without changing the cell formatting to text.
The current cell format is number with no decimals.

Big G