>Thanks Carlos for the info. Unfortunately all the number I want to convert are 12 digits long and some of them have a minus in front of them. Any ideas ??? eg. 249272136572 which should be 3A09C6F37C or -438183398324 ??? Thanks

I posted a link to a possible solution. At this point, may I ask why do you want to do this? I guess you are reading cattle RFID tags?

Carlos Alloatti