Formula for checking duplicate numbers

[Ron]

I have to record apt unit numbers in separate columns. I could up to 20 or 30
columns. My problem is apt unit numbers being entered multiple times. Is
there something that can check for duplicate numbers and let me know?

Thanks

 

[T. Valko]

If the columns are in a contiguous block then it's fairly easy. If the
columns are scattered around the sheet then it could be complicated.

 

[dflak]

If you simply want to identify where duplicates are, then use conditional formatting. Use the following formula for conditional formatting: =COUNTIF($A$1:$C$4,A1)>1 The range $A1$1:$C$4 will have to be expanded to include the entire range where duplicate apartment numbers could exist. The cell A1 is the leftmost, topmost cell in this range, and the format can be duplicated to all cells in the range.

 

[wcurtis]

Is the duplicates you are looking for in one column? If it is, I insert a
column next to it and use this formula. Just use the correct column letter
you are searching for in the formula.
=IF((COUNTIF($B:$B,$B2)>1),"Duplicate("&COUNTIF($B:$B,$B2)&")","")