org-table-number-regexp

org-table-number-regexp is a variable defined in `org-table.el'.
Its value is

"^\\([<>]?[-+^.0-9]*[0-9][-+^.0-9eEdDx()%:]*\\|[<>]?[-+]?0[xX][0-9a-fA-F.]+\\|[<>]?[-+]?[0-9]+#[0-9a-zA-Z.]+\\|nan\\|[-+u]?inf\\)$"

Documentation:
Regular expression for recognizing numbers in table columns.
If a table column contains mostly numbers, it will be aligned to the
right. If not, it will be aligned to the left.

The default value of this option is a regular expression which allows
anything which looks remotely like a number as used in scientific
context. For example, all of the following will be considered a
number:
12 12.2 2.4e-08 2x10^12 4.034+-0.02 2.7(10) >3.5

Other options offered by the customize interface are more restrictive.

You can customize this variable.