To get the count of values with duplicates in the list, use the following formula:

```
=COUNTA(A1:A20)-SUM(IF(COUNTIFS(INDIRECT("$A$1:" & ADDRESS(ROW(A1:A20),1)),A1:A20,INDIRECT("$B$1:" & ADDRESS(ROW(B1:B20),2)),B1:B20)=1,1,0))
```

Enter this as an array formula by pressing Ctrl+Shift+Enter. This will give you the count in one cell -- no extra columns needed.

You can also return the row numbers of each duplicate entry, but you'll need a little help from a VBA user-defined function (UDF). To create the UDF in VBA, press Alt+F11 and insert a module. Paste the following code into the module.

```
Public Function CCARRAY(rr As Variant, sep As String)
'rr is the range or array of values you want to concatenate. sep is the delimiter.
Dim rra() As Variant
Dim out As String
Dim i As Integer
On Error GoTo EH
rra = rr
out = ""
i = 1
Do While i <= UBound(rra, 1)
If rra(i, 1) <> False Then
out = out & rra(i, 1) & sep
End If
i = i + 1
Loop
out = Left(out, Len(out) - Len(sep))
CCARRAY = out
Exit Function
EH:
rra = rr.Value
Resume Next
End Function
```

Now, to get the list of row numbers of duplicates, enter the following formula in a cell:

```
=CCARRAY(IF(COUNTIFS(INDIRECT("$A$1:" & ADDRESS(ROW(A1:A20),1)),A1:A20,INDIRECT("$B$1:" & ADDRESS(ROW(B1:B20),2)),B1:B20)>1,ROW(B1:B20),0),", ")
```

Enter this formula as an array formula by pressing Ctrl+Shift+Enter.

You can also use this UDF to get a list of the actual values that have duplicates. The following formula will work for this purpose:

```
=CCARRAY(IF(COUNTIFS(INDIRECT("$A$1:" & ADDRESS(ROW(A1:A20),1)),A1:A20,INDIRECT("$B$1:" & ADDRESS(ROW(B1:B20),2)),B1:B20)>1,A1:A20&" "&B1:B20,0),", ")
```

Also enter this as an array formula.