[Mr KT]

Hi Tuska,
try this (just with regular expressions radio button on):

(?<![0-9])[24](?![0-9])

Explanation:
(?<![0-9]) means negative look-behind, check no number before 2 or 4
[24] means find 2 or 4
(?![0-9]) means negative look-ahead, check no number after 2 or 4