Formula is: =COUNTIF(C:C,C1)1

Regards

Trevor


"souris75" wrote in message
...
Hi I have a huge amount of number to enter in the C column. I want to be
sure to not enter the same number twice. Is it possible to have a formula
who can retrace the number (if it's enter twice) and to change the color of
this number? It's been almost 2 days.... and by the way:

NB.SI (C:C;C1)=1 is not working even in conditional formating or in
validation.
Thank you.