My Last Number Is Always ZERO. What Gives?

So, I have your standard bookkeeping spreadsheet... One of my pages has Account Information such as Account Numbers, Contact Phone Numbers, Website Addresses, etc...

When I put in the Account Numbers, no matter what I do, after I hit <ENTER>, the last digit turns to ZERO.

Why is this?

Example:
I enter 1234567890123456
BUT
The cell shows 1234567890123450

I have gone to FORMAT CELLS and under the NUMBER tab I select Category NUMBER

How can I get this to display correctly?

Ahhhhh! That was simple! Thank you very much