Automatically place square brackets around a number

[Thisguy]

How can I format a cell so that when I type a number in the cell it will appear with square brackets around it.

Ex. When I enter '2' in a cell, I want it to appear as '[2]' (without the quotation marks obviously).

 

[Seti]

Use custom cell formatting with this:

"["0"]"

Adjust if you need decimals or commas or negative numbers.