Convert Unix Time Stamp to Date

I am getting external data with a Unix time stamp (number of seconds since 1/1/70... the Unix epoch). I have used a formula field to give us the right date serial number. This formula is:

(createdTime/86400 + 25569 + (-5/24))

The explanation for doing this in Excel is here (http://spreadsheetpage.com/index.php/tip/converting_unix_timestamps/)

Now, since the formula is a number, how do I then convert it to dd/mm/yy format?