Cell entry changes

I am using 2003, a column that is fromatted as general with no sample entry that is to be confirmation numers is changing on its own. I type in 12103526713 and when I move to the next cell that entry changes to 1.22104E+11 which is meangless. What causes this and how do I prevent it?

Tried that and auto format as well, no chnage. Space is not the issue, I have left several extra spaces in the column.

The cell width is set to accomadate 16 characters I am only trying to enter 12 so size is not an issue.

Something strange is going on, if I enter 122103526713 or something like it the change occurs. If I knock off 1 digit everything is ok, there seems to be an eleven didgit limit to the cell, size has no effect? If I add a twelveth digit or more then the entry changes. Is excel limited to 11 digits per cell?

That worked and it still allows me to enter a confirmation that contains letters. Thanks much!