Allow Number field to enter specific values

[Mathiyalagan]

How to configure the number field to allow only specific values like 2,8,10,12 not other values.

[Nic Brough -Adaptavist-]

Code. 

You need to either find (or write) an add-on that process a field that only accepts integers,  or alter the way the standard number fields work by injecting something.   I would use script runner bahviours  to do that